Warhammer 40,000/WMG

Chaos has already won
Think about it. They're gods of chaos, and what place is more chaotic than the Warhammer 40k world? There's more than enough war to sate Khorne, scheming for Tzeentch, hubris for Slaanesh and Despair for Nurgle as it is, and it's basically a giant hell already. All the fighting is just the four chaos gods reveling in their own chaos-ness and playing off the mortals against each other for the lulz.
 * Jumping off that, the Imperium NEEDS Chaos. With Us or Against Us is pretty much the life and blood of the Imperium: if you're not with the Imperium you'll succumb to Chaos. Without the Warp and the mutations and other unfun things, the Imperium would eat itself alive in civil war. With nothing outside, the Imperial Guard, Space Marines and Imperial Inquisition would come to blows.
 * Each Chaos God needs other Chaos Gods and the Imperium as well, because if Chaos should destroy the world and kill all sentient life, then it ceases to exist. So, they let much of the sentient life and the Imperium live, farming emotions and prayers from them.
 * However, one can easily argue that Chaos has lost. Yes, there is lots of death and destruction, but it has been consistently death and destruction. None of the major factions besides the Tau (and to a smaller degree the Eldar) have changed much in 10 thousand years, leaving things in a stable (if very violent) status quo. Thus, order exists. Bloody, horrifying, violent order.
 * When the status quo is the propagation of destruction and thus change it can be counter-argued that Chaos has won even then. Furthermore, Chaos in Warhammer is quite different from the conventional idea of Chaos (the conventional idea being, for want of a better term, transition/disorder), and as long as the Gods are fed their fill, they have won. Khorne in particular, stands to gain the most from every waking second of existence. He's the God of War, after all. He and his worshipers will ALWAYS win, if things keep going as they are. And if they don't, he'll continue to win on a slightly smaller scale. Whenever someone even raises their voice in anger. In truth, the only god who could stand to lose from the consistency of the setting is Tzeentch.

The entire galaxy is stuck in the 41st Millennium thanks to the Warp surrounding the galaxy.
Games Workshop has hardly progressed the plot from the 41st Millennium. It's because Chaos gods know if everyone gets killed as the world gets worse, they would also cease to exist. So, with the unimaginable power of the Warp, Chaos gods has stopped time from moving, eternally sparring mortals for fun and evulz.

Empy is the Chaos god of Fanatical Zeal.
Being a ridiculously high powered psyker that even the Chaos Gods feared must hint at the insane presence he has in the warp. Hell, the Astronomican was powered by him before his interment in the Golden Throne. His body withers but his warp presence grows ever stronger, fueled by the fanaticism and zeal of the Imperium. Not only that, but any alien which shows emotions of righteous zeal is also indirectly feeding Empy.

The Chaos Gods, the Emporor, anything originally from the warp, is God/Jehova/Allah/ etc.
Since in any culture with a supreme being, that being created everything (all matter and energy, anything that has a soul had it given to them during development by them.)thus they created love, happiness, beauty, etc. Unfortunately, they also would have to have created hatred, rot, massecre, etc. In the future, Satan (or his equivalents in other cultures) wages his war against this supreme being of your choice. He is defeated, but only after the being embraces his/her/its darkness. This darkness, now dominant, compartmentalizes itself into numerous individual "gods", and its light, slightly tainted by the darkness, emerges to lead the species it had chosen before, humanity.
 * Dude, that's impossible in so many ways. Firstly, the Emperor is the result of a combination of a few thousand psykers. Secondly, the Chaos Gods came into existence in the Middle Ages except for Slaanesh, who appeared during the Dark Age of Technology, due to the emotions of mortals. Thirdly, why would a fragment of god seek to stamp out all religion?
 * No, the shaman thing was but one of many explanations being thrown around. It is still unclear what the Emperor truly was. Secondly, time means nothing in the Warp. They manifested and gained their sentience at the very dawn of Creation, but that translates to trillions of years later in the material universe. They have always been sentient, and yet, have never truly been so to mere mortals. Confused yet? Well it's Chaos. Lastly, The EMPRA decided to stamp out Religion not because he thought it was 'STUPID AN' EVUL', but rather because he knew that there were certain gods in the galaxy and decided that if he allowed Humanity to continue to go down such a path, it would eventually lead to them meeting with said Gods. And also, he thought that if people stopped believing in daemons and shit, they would eventually go away. What the Great Throne Vegetable didn't realize is that Chaos is fueled by sentient thought, not explicit belief. Just clearing that up.

The Adeptus Mechanicus is the real power in the Imperium.
Think about it; The Adeptus Mechanicus has a pretty strong to a massive presence in every other Adeptus/Adepta, Officio, and Departmento in the Imperium. The Adeptus Mechanicus is capable of being completely independent from the rest of the Imperium if it choosed to be as it has all the production capacity, military might, organization, population, and resource pool to survive on it's own, though it may be somewhat diminished from secession; but the Imperium of Man would probably not survive without the Adeptus Mechanicus, and in fact the Adeptus Mechanicus can more or less destroy any other organization in the Imperium on a whim by simply withdrawing all support from it while the AM would be far less affected if another organization tried this with them. So it stands to reason that in reality, it is the Techpriests and not the Administrators, Generals, Inquisitors, Chapter Masters, or what have you who hold all the real power in the Imperium and it is Holy Mars, not Holy Terra that is the center of power in the Imperium of Man.
 * Makes sense, given how much primitive and backward the Imperium is without the Adeptus Mechanicus.
 * Keep in mind that the Machine Cult still needs the rest of the Imperium for supplies and the like. Forge Worlds need to import food and so forth. Plus their armed forces (while powerful) lack the sheer numbers to defend themselves from all the threats they would face without the assistance of the Guard/Navy/Marines/Inquistion/etc.
 * And that some SM Chapters are pretty self sufficient and tech savy on their own.

The four chaos gods were all once mortal
The chaos gods were specific people and acted like their profile.
 * Slaanesh= Eldar obviously
 * Nurgle= Necrontyr
 * Perhaps more likely the Tyranids... "plague" can be used to refer to insects as well as diseases.
 * Khorne= Human Orkz
 * Khorne being created by Humans is canon, from the Daemon Codex. His first and most powerful Daemon Prince was once a human as well.
 * I knew about the human daemon prince it pissed off atleast one person for implying that it was Genghis Khan a national hero to your average person from Mongolia being the only mongolian anyone outside the country knows the name of.
 * As a descendant of Changheiz Khan, I thought it was rather badass.
 * Tzeentch= Nobody knows because his profile doesn't fit any mentioned races
 * They probably schemed each other into extinction.
 * Perhaps they're the Old Ones? I mean, we're talking about a race who created the Orks to save the galaxy from destruction. To even consider such an option, you'd have to be a truly dedicated customer of the Gambit Roulette...

The entire games backstory is imperial propaganda
The real good guys are the Necrons.
 * Don't forget the Tau.
 * Since the Tau seem to be the goodiest of the races, that means that they actually make Chaos look like mischevious schoolchildren.
 * Then the Orks are a race near extinction and not infesting most of the galaxy.

the Squats aren't Extinct.
The last survivors of the Squats managed to escape extinction from the Tyranids, though they have lost most of their technology and history in the process. Stranded on a forgotten Feudal world enveloped in a warp storm, they spend their days building elaborate fortresses with magma based, lever operated traps powered by burning cats. Among the survivors, a very powerful cult devoted to Khorne has sprung up, who they call Armok...

WH40K has Tommy Westphall Syndrome
The "Emperor" is not really the emperor of anything. He is in fact an autistic with a nigh superhuman imagination who has created an entire fictional universe within his mind. This theory explains every self-contradiction and discontinuity in any piece of fluff ever. As for the Emperor himself: what better metaphor for severe autism than a man, perfectly awake and sober, yet unable to talk, move, or even survive without intervention, unknowingly victimized by those who misunderstand him (the Imperial Cult), slowly dying in a world that is nightmarish, bleak, and incomprehensible?

The 'Binary' used by the Adeptus Mechanicus is, in fact, l337.
Quick Summary of Binary: Binary is a language used by among the Adeptus Mechanicus, which is used to differentiate the their members from those who are not, and is a jealously guarded secret among the Mechanicus - the point where a character has said (quite seriously) that he would have to kill his non-Mechanicus friend if he were ever to decode the Binary language.

The Adeptus Mechanicus are a group of elitist 'players' or 'priests' - the l337 - operators of machines (computers or tanks) who look down upon those who are not knowledgeable about the machines - the n00bs - and value their machines more than the lives of others, or themselves, and wish to incorporate themselves more into these machines - using headsets to chat, implanting hard drives into your spine - and practically worship them.

Also, they absolutely hate any unorthodox or innovative methods of operation as it would make them redundant/put at a disadvantage. For the AdMech, its new machines, for the l337, its hacks/h4x. Offenders are often never given a second chance - by death or by bannage, you will not do that again!

When l337 is used around n00bs/non-adeptus Mechanicus, l337 sounds like complete gibberish; this is tricky to justify when l337 is verbalized (as opposed to written, which is easier to decode), but it may be because they 'speak' in the binary forms of the letters/numbers that they are using, as a double-substitution cipher, as regular binary (11010010) would be relatively simple to decode once anyone got a hold of a method of translating those binary codes.

Of course, as Warhammer 40,000 has a lot of tropes Turned Up to Eleven, its no surprise that the repercussions of translating l337 is a lot less permanent than that of the Adeptus Mechanicus.


 * You know this actually makes sense, and explains how they've lost so much knowledge.
 * More to the point, it explains why the Inquistion has never cracked the code. Binary would be brutally easy to crack with a calculation machine, but 1337 would be uncrackable without AI or a human involved. Given that they feed the 1's and 0's in to the machine, and get nothing a machine can read as a language out of it...

The Emperor is Kane from Command & Conquer.
Highly charismatic, possibly immortal, manipulation of various ideologies to achieve Nod's max appeal, born thousands of years before Christ. Plus the whole abrahamic Cain & Abel thing going on could be a nice bit of backstory. Plus the setting's already grimdark, and there's a lot of nice proto-Baneblades.

Jesus is The Emperor.
A man who has lived since the beginning of humanity, is the most powerful psychic mankind has ever know and defeats evil in the penultimate battle, paving the way for his empire to rule for millenia. And he's always watching you.
 * And Christians are the Imperium. Christians put him in the cross and waged world war against every culture under his name.
 * The Imperium of Man does sound like the Roman Empire / Holy Roman Empire, concerning Warhammer 40000 had a lot of Latin terms....
 * Seeing as how the Emperor disguised himself as various influential people throughout time, there's a very good chance that, historically speaking, Jesus was The Emperor. Or, accounting for personality changes, anyone else.
 * Going by Graham McNeill's Horus Heresy book: Mechanicum one of these influential people was St George.

The Antichrist is the Emperor.
After the establishment of the star-spanning human empire in the Dark Age of Technology, it collapses as Earth is engulfed in a massive warp storm -- which is actually the second coming of Jesus and heralds the Apocalypse. However, Jesus is defeated, the storm abates and the Emperor leads an army to forge the Imperium of Man. Also after the war, two of the Four Horsemen (Pestilence and Death) escape Earth and flee into the warp, becoming the Chaos gods Nurgle and Khorne. The Emperor enslaves War and uses him as the template for the Space Marines, while he himself is Conquest.
 * Nurgle and Khorne (and Tzeentch) have been around for a long, long, long time, so they couldn't have appeared as recently as the happenings on Earth. Also, while Nurgle certainly fits in with Pestilence, Khorne is more a god of battle than Death.
 * Not to mention that it is explicitly mentioned that the "Hood and scythe" depiction of death was actually ingrained into the young raced by the Nightbringer, and that he is literally why they fear death.
 * Also, from the start of the Great Crusade to the end of the Horus Heresy was 210 years. That's 3 1/2 periods of 60 years each (a short-end human lifespan), and then he was mortally wounded. And now he's worshipped as a god. Mind, he's spent more time dead than reigning, but if he were to revive, would that lead to 210 years of Jehovah's wrath followed by the return of Christ?

The Emperor is Doctor Doom after the events in "What If Doctor Doom Kept The Beyonder's Power."
In the issue, Doom becomes   Doom, in this reality, has his face restored, and has been possession of great cosmic power for centuries. Civilization has already fallen once, hostile alien races have been subjergated or destroyed by his power. Is it so unlikely that his power returned to him, and he then led humankind back to the stars as the Emperor of Mankind?

It's gonna get better.
Since the 5th edition put the game into so bad that there's really not much pushing left, Games Workshop now has an excellent opportunity to pull out something totally unexpected and make everything loads better in one go. Because I dunno about you, but all this darkness makes the whole thing kinda depressing, and why would you want to play with anything other than Tyranids or Necrons since you know one of those two is gonna win the whole thing in the end? Anyway... "The Emperor: I'm da biggest, dat means I'm da boss!"
 * In one of his inexplicable Xanatos Gambits, Tzeentch tricks Khorne into assassinating Slaanesh, allowing every single Eldar soul imprisoned by him to get free. Some of them finally get to the afterlife, while the others, including Eldrad Ulthran, stay, get a new physical form, and help to rebuild the Eldar back to its former glory. In addition, the psychic backlash resulting from this instantly brings their new god of death to life. Oh and, with Slaanesh gone, they also finally get to relax a bit and have a little fun, though definitely not enough to create another nasty god.
 * The Golden Throne, thanks to all its flaws, finally breaks up for good. However, instead of the Emperor dying, he actually wakes up, and begins his quest in leading the mankind from darkness. With him awaken, the Astronomican powers up again, and no longer needs souls to work. Also he relaxes a bit of the Imperium's attitude to "Xeno Filth", allowing them to establish diplomatic relations and some trading with the Eldar, Tau, and even Orks, although the races are still a bit hostile to each other.
 * Highly doubtful that the Emperor will be tolerant of aliens thats been tried.
 * Actually, its a well known fact that the Emperor's beliefs were manipulated and he never believed in all of that Space Nazism that the rest of the Imperium believes. The priests of the time entombed it, created those false claims, and because he was a being of such power (basically a human God) everyone in the Imperium was too scared to doubt this and believed the Priests. That and if they didn't they'd probably suffer a mild case of deathness.
 * No, but he COULD lead humanity into crushing the two greatest threats to it, the tyranids and necrons.
 * Actually, the Emperor was Anti Xenos. Just not anti mutant. And he didn't execute HERETI-well. I suppose that's debatable. But yeah, no matter what happens after the golden throne breaks, it makes things better. If The Emperor dies, he will either be reborn and lead humanity to the stars, or send out such massive psychic backlash, literally EVERY Eldar, most Orkz, a good number of humans, and ALL Tyranids within the milky way would die. That's a good thing because all of those suck, that, and it would mean Nids would lose a beacon (they home in on the emperor), and would go for another immense psychic power, likely in the eye of terror.
 * The Emperor shall enter the warp where he will become a REAL GOD. Then, he shall collect the souls of his bravest warriors, just as chaos collects the souls of its followers. The Emperor shall also either convert existing daemons into, or just make out of thin air, ANGELS THAT SHALL BATTLE BESIDE THE SOLDIERS OF THE IMPERIUM. But before all that soul collecting, he'll do something he's wanted to do for thousands of years: Bring his son back to life. Ass obliteration shall commence then.
 * If you believe that the Legion of the Damned are the dead spirits of slain space marines, then the first part is technically true
 * well then all that's left is for a redeemed Horus.
 * Some more Standard Template Constructs are discovered. In addition, the Tau and the Eldar find a couple more, and (after the Tau reverse engineer the hell out of them) sell them for humans with a moderately high price. With them, the Imperium's technology advances with some gigantic leaps.
 * With the friendlier attitude of humans and Eldar to them, the Tau can spread across the galaxy far faster than ever before. Some of them even go and hitchhike across the galaxy along in human and Eldar ships, all the way to the other side of the galaxy. And of course, their technology is getting better still.
 * With Slaanesh gone, the Laughing God emerges from the Webway, and travels around in his quest to find every single piece of Khaine and glue him back together. Khaine returns as well, and together the gods of Death, War, and Trickery, lead the Eldar against the Chaos and Necrons.
 * But then it's going to get a tad worse as well: The Dark Eldar join forces with the Emperor's Children, as both have lost their god and are all alone and orphaned. They travel across the Webway with no direction or goal whatsoever, fighting absolutely anything and everything coming to their way, being now utterly and compeletely unpredictable. Oh and, as the Emperor's Children learn of the Webway, they give access to it for all the other Chaos Marines as well, who use it to strike just about anywhere. Abbadon's 14th crusade goes through the Webway, allowing him to go past Cadia and appear all of sudden at the other side of the galaxy.
 * Wait, but don't Dark Eldar hate Slaanesh ever so bitterly as (s)he hunts their souls as well as ordinary Eldar ones?
 * Yes, that's an important distinction: The Dark Eldar are not Slaanesh worshipers; they're Slaanesh appeasers. With Slaanesh gone, they won't get nicer, but they may mellow out a little simply from the relief of losing their source of existential dread. In any case, the Dark Eldar are, right now, as bad as they could possibly get, and they were never portrayed as a cosmic threat. You certainly don't want to be captured by them, and they have a good claim to being the most evil faction in 40K (their codex even claims that they are, but its to be taken with a grain of salt because it was printed back when Churchill was PM), but they're quite possibly the weakest and least threatening race on a galactic scale.
 * The advance guards of the Tyranids and the Necrons suddenly get their asses handed to them by the temporary alliances formed by the Imperium, the Eldar, and the Tau. The Necrons become compeletely pissed off by this, and wake up every single one of their tombs all at once. Meanwhile, the main attack force of the Tyranids turned out to be a lot closer than anyone thought, and finally appears to the edge of the galaxy.
 * The new Imperium-Eldar-Tau alliance manage to do this by manufacturing really cheap gun and armor "prototypes" and "accidentally" have them fall into the hands of the Orks with an instruction guide with the very specific wording that the guns WILL cause Necrons and Tyranids to explode into a fiery mass of gore in one shot and that the armor WILL reflect all damage back to Necron and Tyranid attackers, causing them to explode into a fiery mass of gore.
 * And are greatly disconcerted by the fact that the Orks can't read.
 * Make it a picture book?
 * The final awesome battle begins.
 * Not nearly GRIMDARK enough. Also, no plan for a lighter, (even if it never gets better) ending is complete without CIAPHAS CAIN, HERO OF THE IMPERIUM!
 * Caiphas Cain will be sent as a laison to the Tau due to his actions in For The Emperor. He will accept this because it will be a nice safe diplomatic mission far from the fighting. It will of course not go that way at all
 * It will also involve Ibram Gaunt. And yes, he and Cain will get to do Back-to-Back Badasses. The sheer awesome (and Ciaphas's snarking) may be enough to kill one or more of the Traitor Primarchs.
 * The power of the awesomeness also brings Lord Commander Solar Macharius (He was just hiding), and he is once again placed in command of the Imperial Guard, with Cain on his right, Gaunt on his left, the Emperor behind him, and billions of soldiers before him, the Guard surges forth as an inexhaustible wave and purges the alien filth from our Galaxy once and for all!
 * Hey, let's not go crazy. Old Mac was a swell guy, but he ain't Commissar Cain.
 * Oh get over yourself with Cain. Macharius conquered a thousand worlds in 10 years, he is FAR better. I would also like to add that as part of this whole thing, Commissar Yarrick finally finds Thraka and crushes the life from him. Then and only then does the old man allow himself to die. He receives the greatest funeral since Sangunius and is buried on Terra itself.
 * Just to point out how much more awesome Macharius is, he conquered those thousand worlds in 7 years, 30% faster than any less awesome lesser-mortal might have done. And he never gave up; the Guard did.
 * It all depends on who things are getting better for. This troper, for one, can easily see the Imperium getting its act together and beginning the pwndernation the incoming Necrons and Tyranids. Also, Abbadon? This troper thinks we should be keeping our eye on Ahriman. last we heard of HIM, he was trying to find stuff out about the Eldar's webway...
 * Diplomatic relations? With Orks? One may as well try to open a dialogue with a Khorne Berserker.
 * Ah, but you can hire Orks as mercenaries if you've got enuff teef on hand.
 * Or alternatively the Emperors awakening will send shockwaves throughout the the Warp, causing Orcs to transform into a proud warrior race, and making them more civilized, and more like what the Old Ones had in mind in the first place.
 * And their Leader will be Warboss Thrall, with his looted daemon hammer.
 * Let us not forget the primarchs. First among them, Leman Russ wonders back onto the scene where his Wolves will proceed to get a morale boost big enough to take on a several planets worth of Chaos all at once.
 * Also, Commander Farsight turns up, the first tau psyker, using reverse engineered Eldar tech and goes on to create an army of Kroot psker's with force weapons.
 * I've imagined a breed of Tau Plasma Warriors. They're basically the Tau's (or just Farsight's) attempt to imitate the Space Marines. They're Tau Fire Warriors with a mishmash of genetic augments and splicings from Tau aligned species.
 * Alternatively, the thing the Tyranids are fleeing from reached our galaxy...and it turns out to be a cosmic force of love and goodness that makes everybody get along voluntarily.
 * You, my good sir or ma'am, are amazing, and I award you an internet.
 * In the pleasant lightness of the 42nd Millenium there can be only peace!
 * Better idea: Rather than opening up diplomatic relations with the orks, the Emperor has discovered how to "tune" his psychic power to mimic the Ork Waaagh. The orks think he's Gork or Mork (fight each other over which one), and he sends them against Chaos, the Tyranids, and the Necrons.


 * Or the Emperor uses his psychic powers to convince the 'Nids that the Eye of Terror is a fat free, low cal buffet and beer garden. Hive Fleet splinters flock to it, the "Shadow in the Warp" plugs the Negative Space Wedgie long enough for the Space Marines to trounce several factions and convince the Tau that there is something to Chaos. Travel in the warp becomes easy. By the time the Chaos gods re-open the eye, their forces are weakened and the 'Nids equate our galaxy to spoiled food.
 * If it gets better, it will get better in a way to sell more action figures. So -- the miracle working of the living saints suddenly starts to manifest plentifully and all over the place, and even gets better, so they can protect psykers against taint and purify tainted planets. Massive crusade against Chaos is feasible. Plus unleashing a lot of new psykers against orks and tyrannids. Plus the Inquisition and Church won't like it, so you can have fighting there -- especially if people protecting psykers get annoyed about the Black Ships, or if seccessionists get their hands on the miracles, or both.
 * Oh, and this includes healing miracles. The obvious way to attack the necrons is to "heal" them. They aren't so formidable in the flesh, without all that metal. It does have the disadvantages that necrons out of healing range will be kinda annoyed. (In-universe disadvantage. Out-of-universe: More action figures!)
 * Or it will escalate once the God Emperor gets-up/dies making the chaos work 10 times harder to hold him off by haing the gods ally and create units with composite traits of gods, the orks will get more dakka (perhaps, maybe, if it could, something close to in some way, enuff dakka), more of the nids will show up cause GE is is 100X more a psychic beacon when walking then before thus bringing new unit types in, the tau finally get the wrap stuff down and become 1337 at using it, the eldar have a conference and pool their resources to build greater wraithbone stuffs, it turns out the GE was sitting on the new dark eldar codex and someone yoinks it once he gets up, the necrons wake up some more horrible contraptions (possibly as a response to the massive wrap signature), Space marines get GE as an HQ + gear to match his great crusade + maybe another founding, Sisters split on the inside (GE was against being a god) so 1/2 stay rather similar but another 1/2 become much more calm and professional, IG gets new tanks in his name, did I miss anyone? PS Ciaphas Cain, HERO OF THE IMPERIUM, get a model as the god emperor's human champion as Warmaster Caiphas Cain, His Emperor's Hammer. Had to have Cain involved.
 * Yes, you missed the missing Primarchs. What the heck, all the missing primarchs, including the dead loyalist ones. The souls of all the Imperial faithful have indeed been taken in by the Emperor, and will manifest themselves in this fight. Ciaphas Cain, Ibram Gaunt, the whole nine yards.
 * Someone will FINALLY acquire enuff Dakka.
 * There is NEVER enuff' Dakka!
 * Further evidence that it will get better: recall that the 40k 'verse is essentially a Darker and Edgier version of the European Dark Ages, turned up to eleven and IN SPACE. All the loosely connected, inter-warring states are held together by a paranoid, anti-intellectual and Orwellian Corrupt Church that burns heretics and generally does exactly the opposite of what their martyr-god intended. They have an extremely dim view on the inner workings of the technology left behind by the civilization they crawled out of the ruins of (Rome/the Dark Age of Technology). The elite Space Marines are the Knights bravely serving their God by killing anyone who doesn't comply to their standards of species, genetic purity, and faith. The Eldar are the Pagans who once flourished before the advent of the Imperium, but whose civilization is now facing extinction (like due to being burned by the Church as witches), and we have the Dark Eldar/Orks as the pirates and war-obsessed Norse barbarians, with the Dark Eldar covering the rape and Orks covering more of the pillaging and burning. And the Necrons and Tyranids kind of both combine to represent the Black Death, what with the 'nids parasitically devouring everything like a plague, and the 'crons for carrying the imagery of an inexorable, implacable, menacingly slow-walking Death that the bubonic plague was associated with. Meanwhile, the Tau is of course the burgeoning Asian Civilizations (like Ancient China, India and the Arabic civilizations) which despite being isolated managed to flourish while the once-glorious West burns.

Why does all this mean that things will take a turn for the better? Well, because since this is the Dark Ages there has to be a Renaissance!!! Why all of this? Because History repeats itself.
 * That means Warhammer 40k will end like this: The Imperium deposes the Corrupt Church (most possibly through the awakening of the Emperor or after a terrible Nid/necron-induced apocalypse, or we can do it as Real Life had done it, through the the discovery of an STC that describes the Scientific Method in all its glory), succumbs to an explosion of intellectualism and rediscovery, discovers a new warp drive that doesn't rely on passing through the Warp itself and is infinitely more reliable, and expands across the far reaches of outer space where no man has ever gone before, ultimately reaching a galaxy far, far away where a new republic is established. The Tau will probably have new advancements in technology, establish a powerful empire "For The Greater Good" and become powerful rivals or allies against humanity. Eldar would also try to make their own empire to rival or become allies with the Imperium and Tau. With the Age of Reason revived, more and powerful weapons are developed, and the Imperium, Eldar and Tau, with some Orks, would be allied against the 'Nids, Necrons, sundry other Eldritch horrors that besiege the galaxy on all sides, or other rogue Ork waaaaghs. Of course, there's no modern world if it wasn't for some vestigial remnants of the old Imperium that are lead and reunited by a megalomaniac who is as powerful as the Emperor in terms of psychic powers and charisma, yet is an utter psychopath like a combination of Chaos and the past Imperial church, which causes the final awesome battle that will decide the fate of the Milky Way Galaxy.
 * Also, with the death of the powerful chaos-corrupted megalomaniac, two ways of life will emerge as dominant. One is the old secular economic system of Terra during the Dark Age of Technology, the other is the philosophy of the Greater Good, with the Tau having used the Great War to establish itself as a superpower. To seal permanent communication with all sentient life that exists, humanity created a massive network (probably what the emperor originally intended, a Webway Network through the Warp). Meanwhile, after being exterminatused, the Eldar started to redirect their squicky ways to the creation of new popular media (while the Dark Eldar opted for the alternative), and it proved too efficient, being popular throughout the said network. The rest of Chaos (except for Tzeentch) was ultimately sealed and split between two rival groups: a squick-infested wretched Hive Mind in the Interstellar Network, and a small cult of xenos. The "Greater Good" soon proved itself inefficient, the Emperor and the Chaos Gods start to lose their powers and popularity most likely due to that person, and meanwhile at the new republic in the galaxy far, far away Tzeentch took the form of a black man.....
 * Alternatively, Tzeentch (the god of HOPE) turns out to have been Good All Along, his insane and seemingly pointlessly complicated plans were actually instrumental in preventing the other 3 chaos gods, the necrons, and the tyranids from gang raping the rest of the galaxy.
 * He does that for all races actually. If everyone dies he has no one to change their ways. If the world wasn't crapsack no one would have hope, because everything would be all right. He needs to keep everyone at the status quo to foster hope AND change.
 * If any of the theories about the Imperium, the Eldar, and the Tau forming an alliance come to pass, a band will be formed with members from all three races and they will play a cover of Iron Savior's "Predators". Because if things are getting un-grimdarkified then the forces of good/order will need some heroic music.

It's actually gonna' get worse.
I don't know how, but it will happen. It just will.
 * Theory: There is a massive Necron army buried somewhere in the Solar System, probably on Mercury or Venus. They will awaken along with the Void Dragon, and sterilize the Solar System. This effectively destroys the Imperium. Most of the human race will be wiped out. The survivors will be forced to ally with various alien races. New factions that will receive codexes:
 * Cadian Empire: Largest human faction, ruled by Chaos Lord Creed (who has pledged allegiance to Tzeentch). Military structure based on the Imperium.
 * Clan Armageddon: Ork/human fusion, led by Warboss Yarrick after he took over Ghazgul's horde. Basically Orks with better weapons, and backed by humans in tanks.
 * Gue'Vesa: The Tau Empire has effectively doubled in size, and frequently deploys human soldiers to support their Tau infantry.
 * Craftworld Terra: Perhaps the last true Imperial loyalists, including the Blood Ravens. Allies of the Eldar.
 * Theory: The Harlequins will finally succeed in reconciling the Craftworld Eldar, the Exodites, and the Dark Kindred; and with the help of the Laughing God will combine their Waystone, World Spirit, and soul-stealing abilities to jump-start the creation of Ynnead, strengthening him with the souls of their fallen enemies. They will then re-assert their place as the lords of the galaxy in an orgy of destruction the likes of which has never before been seen; while using their reborn powers to make their ork puppets into a vast and impenetrable shield against the encroaching Tyranids.
 * Other Theory: At some point the Tyranids chow down on a few Chaos Worlds, and the devouring of all that daemon-corrupted Warp-infused flesh has an expected effect on the evolution of the Tyranids, who absorb and adapt to whatever they eat. The newest unstoppable horror of the 41st millennium: Daemon Tyranids.
 * The Tyranids and the Necrons (really their masters the C'Tan) cut a deal: The 'Nids hit Imperal Worlds while the Necrons attack the Space Marines (and their Chaos counterparts), Eldar, Dark Eldar and Orks. They split the Tau. The Nid's get to NOMNOMNOM their way to Terra and the Astronomicon, the Necrons get to see most life purged from the galaxy. Chronic Backstabbing Disorder kicks in, but not before several forge worlds and whole armies are wiped out. By the time the Necrons and Tyranids turn on each other, the forces of Chaos have the upper hand.
 * Theory for it getting worse: things will get so grimdark that whatever remains of the Imperium of Man, the Eldar Craftworlds, and the Tau Empire will be forced to work together to hold back the tide of eldritch horrors, et cetera, that beset them on all sides. It works out pretty well...until a heretical Commissar Yarrick emerges from the Eye of Terror, driven mad by the Warp and leading a horde of Chaos Orks to unite the rest of the Ork clans and crush every other faction in the galaxy. And then they get eaten by Tyranids.
 * And then the Necrons kill all the Tyranids. The universe ends.
 * Good game!
 * Because the universe has been cleared of all life, every link to the warp is closed off. Then, somewhere, someday, Terra develops life without the help of the Warp and suddenly discovers how to make fire. Cue the real world happening.
 * You win one (1) internets.
 * Just see The Shape of the Nightmare to Come.

Everything's going according to keikaku!!!
Everything is going, more or less, as planned for old empy, perhaps he didn't intend to get quite as injured as he did, and yes magnus bursting in trashing one of his biggest projects with his good natured bumbling probably wasn't something intended, but by and large things are going pretty well for the Emperor. Sometime during the Great Crusade The Emperor discovered something that was an even bigger threat than Chaos, could have been the Necrons below mars, could have been Tyranid DNA from a Xenos he dissected in his lab (he is a scientist after all) could be something far far worse that's yet to make an appearance. He deliberatly appeared to do nothing while the chaos gods plotted his downfall because he knew that even a galaxy wide empire of perfect order, wouldn't be enough to save humanity from the bigger bad but Chaos and the limitless power of the warp could be turned against it. Supports the Necron's as the big bad theory since they went into hibernation after losing to the warp in the first place. Though since chaos corrupts maybe he's hoping the tyranids will be corrupted and turn on each other. (feel free to speculate wildly!). An added benefit is that the galaxy, through being in a constant hell, is basically training more and more Badasses through natural selection. As evidence, Empy was more powerfull than 3 of the chaos gods combined (slaanesh came later) which means he was capable of out plotting Tzeentch a fair amount of the time. Also it's unlikely Hourus's corruption and betrayel came as much of a shock especialy since, you know, the emp sat and watched the unborn primarchs get scattered across the galaxy by the warp. Kind of a giveaway that they were up to something.

Akihiko Sanada from Persona 3 is the Emperor.
Goes against the canonical interpretation of the Emperor's origins, but I figured it was worth mentioning. Possible support for this theory:
 * Akihiko is affiliated with the Emperor Tarot Arcana.
 * In the game, references are made to Akihiko wishing to increase his power in order to protect others. The Emperor in 40K uses his powers to keep the Daemons of Chaos at bay (or at least try to, anyway).
 * The Space Marine guardians of Terra are the Imperial Fists Chapter. This Chapter also served as the Emperor's bodyguards during the Great Crusade and constructed the Imperial Palace. Factor this in with the fact that, during his school days, Akihiko was captain of the school boxing team...
 * Akihiko's status as a Persona-user can easily be considered an early manifestation of psyker powers.
 * In Persona 3, Akihiko has white hair. In the world of 40K, several Sisters of Battle are mentioned as also having white hair. This could be a the result of them dyeing their hair as a "mark of loyalty" or even possibly imply a subtle genetic connection. Recall that, before they were the Adeptus Sororitas, the Sisters of Battle were known as the "Daughters of the Emperor."
 * Perhaps Akihiko is an Expy of the Emperor?
 * So what does that make the Protagonist, who was (at least at the time) much more powerful than Akihiko at the time?
 * The Holy Shit to Akihiko's Godlike.
 * Let's see. He spends most of the game gathering power by telling people what they want or need to hear, resulting in enlightenment for both him and the person he's manipulating befriending. He has the power to rapidly switch between various styles of magical abilities on the fly by putting on and replacing personas. His color theme is mostly blue. You get three guesses as to who that makes him, and the first two don't count. Any problems him being the Lord of Change causes the timeline can be handwaved by the general weirdness of time in the Warp. IIRC, Tzeentch has a favored creepy herald/servant he uses as an emissary outside the Warp: it could be Elizabeth, Aigis, or both, elevated to the level of a Demon Prince (although Elizabeth may have qualified as a minor deity to begin with).
 * What would Philemon be, then?

The Emperor is the fifth Chaos god.
In terms of the background, there are many similarities between the Emperor and the various Chaos gods -- his physical body is insignificant compared to his presence in the Warp, human sacrifices are offered to him with tangible results, and so on. Even in terms of game mechanics, he behaves like a Chaos god: all Space Marines get morale check re-rolls that would fit quite nicely as a Mark of Chaos, like the toughness bonuses from Nurgle or the attack bonuses from Khorne.
 * Maybe, maybe not. This is one of those things which will never be resolved because that would end the setting and stop GW from selling toy soldiers. If The Emperor was ever allowed to die, he would either be Dead For Real, and Chaos would swarm out of the Eye of Terror, eat humanity like a snack, and rampage all over the place having all sorts of fun, or ascend to becoming a new warp god, annihilate the four Chaos Gods in an eyeblink and extend the Imperium across the galaxy.
 * The sales problem could be subverted by the emperor ONLY having a presence in the warp, so that the imperium still needs to defeat anything inside the galaxy without his help. Also everything moving towards the galaxy
 * This must mean that either the Emperor doesn't know this would happen, or is trapped in his life support and unable to sever it.
 * The latter has been heavily implied to be the case several times.
 * There's also the factor of how the ascension of a new Chaos God appears to require/cause reality being ripped a new one, decimating the host race in the process. The Emperor may have weighed the benefits of being a Chaos God against Sol being the center of a second Eye of Terror.
 * One of the radical factions of the Inquisition believes the latter part of this theory, and is actively trying to "pull the plug" in order to allow the Emperor to complete his apotheosis.
 * In the "Age of Ending" section of the 5th edition rulebook, it was revealed that Tech-Priests have recently discovered fatal flaws in the Golden Throne far beyond their ability to repair. Also, while the 3rd Edition rulebook had art depicting the Emperor as a withered old man wired to a throne, a similar picture in the most recent rulebook shows the Emperor as a skull-faced, shriveled corpse. Looks like we're going to find out what happens when life support fails soon enough...
 * I don't know what the one down the page is meant to be, but there seems to be a pretty clear Xanatos Gambit possible in this. It takes a whole lot of worship to make a god, right? Well, at the time of the Heresy, the Emperor was only starting to slide to the "god" side of "god-king." So, he makes sure that the Throne will keep him alive for long enough, and, if humanity isn't doing well enough to repair it, it will break down and cut him loose to save them all over again. True Xanatos--bossman wins either way.
 * Another argument for the Emperor already being a god (as opposed to having the potential to become one): he has daemonic servants (angels) that occasionally break into the material world and possess his favored champions (the Living Saints).
 * It's not so much that the Emperor is a Chaos God per se, as it is the case that all gods in the 40K 'verse are basically psychic quasi-daemonic entities existing mainly in the Immaterium. Older fluff indicates that Gork and Mork are already running around in the Warp after all, and they are hardly Chaotic (though Exclusively Evil).
 * There already is a fifth Chaos god.
 * Fine, the Emperor is the sixth Chaos God
 * Maybe the Emperor is Malal!
 * There may be some truth in that. According to The Other Wiki "Malal was at some point cast out or separated from the rest of the Chaos Gods. [...] Malal was perhaps the first of the Chaos Gods and seems to exist only to destroy the other gods and their followers. The Outcast God is both feared and loathed by the other Chaos Gods, and his power may parallel the collective power of the other Chaos Gods. [...] they were the chosen human champions/followers of Malal. Dedicated to seeking out and destroying the followers of the other Chaos Gods" Sound like anyone we know? * coughtheemperorcough*
 * Considering how much the Imperium relies on Warp travel and psykers, both of which are intrinsically tied to Chaos, you may be on to something there.
 * There are more than five already. Another posibility is Necoho, god of Atheists in the setting (I'm serious). According to the Horus Rising series and other sources, before the Heresy the Emperor hated all religion and specifically banned his own cult.
 * The Emperor is the Lady of Pain?
 * Which makes a lot of sense in a world where enough belief spawns new gods (and innumerable demons too) and you know it.
 * In the same vein, he may have become a god against his will.
 * More likely his backup plan. Originally, yes, he was going to weaken Chaos through the anti-religious Imperial truth, then cement everything by sitting Magnus on the Golden Throne to intervene through the Webway wherever a supernatural intervention was needed. When that plan went pear-shaped, he decided instead to take advantage of the worship tickling at the edge of his consciousness, joining with the image of him the Lectitio Divinitatus people were creating in the Warp to become the God-Emperor we know.
 * As far as can be seen, a warp god is no different to a * cough* regular warp entity, just WAYYYY more powerful. Perhaps you are a god if you become powerful enough in the Warp. In that sense, the Emperor could very well be a Warp God, just not one of the very loose chaos pantheon.
 * From what I have garnered from reading fluff, there are lots of Chaos Gods of lower stature then the big four (such as Zuvassin, Murphy's Law incarnate; Necoho, god of atheism, who gets stronger as he loses worshippers), Chaos Demigods so to speak, it's just that the Big Four are the most powerful -in the Milky Way at least- and have the largest cults, so they get most of the screen time... That, and copyright issues have made it hard for Games Workshop to use Malal, as he belongs to the guy that made the (I think) comic book he started out in, and not Games Workshop.
 * They're not really sure who has the rights, which is why they just let it go.
 * Assuming that the Emperor is a Chaos God, he is the god of fear and loyalty. His chosen warriors are freed from fear, just as Nurgle's worshippers are freed from despair.
 * Wouldn't the Emperor technically be the Fourth major Chaos God, since he predates Slaanesh by about 35000 years?
 * Also, if the Emperor is the fourth Chaos God, the five Chaos Gods are personifications of the five Eons from Discordianism. Khorne represents Original Chaos, the war of all against all. Tzeentch represents Discord, the dance of competing intelligent powers. Nurgle represents Confusion, the rise of universal ideology, mass movement, and totalitarianism, also represented by the semi-familial relationship between him and his followers (they call him Grandfather Nurgle). The Emperor represents Bureaucracy, the fall into petty struggles, technological decadence and social stagnation. And finally Slaanesh represents the Aftermath, when everybody falls into hedonist nihilism just before society completely falls apart.
 * Lets look at Chaos theory... The emperor is the chaos god of emergent order. Hope the other chaos gods have read Stephen H. Kellert's In the Wake of Chaos: Unpredictable Order in Dynamical Systems because a big chunk of Unpredictable order with far more followers than they could ever hope for is pissed as hell with them, and the one think holding him back is a life-support machine with cracks starting to show.
 * Okay, I want to make this very clear to... EVERYONE. This isn't FR. As a Chaos God, you're not strengthened by 'belief', you are strengthened by the expression, thought and performance of ideals, emotions, virtues and so forth that have to do with your Chosen portfolio. Just because the all too feared Throne Vegetable has a Cult that numbers in the quadrillions, it doesn't really mean shit if one goes by his powers. If he's truly the God of Order, then gentlemen, he'd be screwed. And that is because there is no fucking thing such as Order in universe like this. And once more, he'd never be able to hold a candle to the Dark Gods, who have trillions of years worth of carnage, scheming, despair and vulgarity behind them which has built up their strength. If there's ANY God more powerful than any other, it's Khorne. Because, you know, this is a setting where the tagline is, THERE IS ONLY WAR. Were the Emperor to ascend to Godhood, he'd be as powerful as any lesser Chaos God. In other words, as potent as the Gods that most Undivided Marines dedicate a spike on their armor to. INB 4 cries of "HERESY!".
 * A. Belief is an emotion. So is fear. Therefore both can technically empower a Warp Entity. B. The Emperor was already as powerful as the four Big Abominations alive. Are you saying that power would just go poof after he ascended?
 * A. Yeah, my point is that people think that the Chaos Gods draw their power from the number of people who have an explicit belief in them. They don't, hell, the Imperium's violent foreign policy has likely done more to strengthen Khorne than any of his faithful's exploits. B. No, he wasn't.
 * If we assume the Emperor has "righteous anger" in his portfolio then Khorne would be somewhat starved by a devout citizen of the emperium. Anger and such over petty or jealous things not so much. If his portfolio also included fear...well< hell he'd be pretty damn powerful from that alone.
 * Any anger at all serves Khorne. That's how the metaphysics of the Chaos Gods' sustenance works. And the reason they've grown so powerful. Also, depending on how you define 'righteous fury', Khorne's followers and the average Word Bearer has it in droves. Khorne's followers tend to be the most idealistic of Chaos Warriors, they believe they exist for nothing else but glorifying Khorne through glorious battle, after all. For example, Angron is turned to Khorne by his burning fury and obsession in avenging his fallen companions. Sounds pretty 'righteous' to me. Furthermore, in a recent Horus Heresy, it is revealed that the Emperor knew from the start that no matter what he did, Horus was gonna tear him apart. So he's likely not as high on the divine totem pole as is implied.

The changes to the Grey Knights' background in 5th edition are a revisionist history written to cover up a political schism

 * In the current Codex, there are supposed to be 800-ish Grey Knights led by eight Grand Masters, and they've got a Purifier Order and a Supreme Grand Master elevated above the rest. In the old Codex, there were closer to 3,000, they didn't have a super-elite Purifier Order, and the whole thing was run by a council of twelve Grand Masters. The other 2,200 Grey Knights and four Grand Masters can't have abruptly vanished overnight...
 * When there was a proposal to raise Draigo to the newly-invented rank of Supreme Grand Master, a lesser portion of the Grand Masters with a strong backing among the traditionalists of the Order opposed it on the grounds that Draigo was an arrogant bastard with delusions of grandeur badly in need of seasoning, not somone who should be abruptly jumped up in the ranks for no good reason. The majority managed to force the measure through, but a good portion of the Grey Knights up and left after that and are now operating in scattered bands working for the Inquisition.

The Tau are the creations of the Old Ones.
First, a warp storm conveniently cuts the Imperium off from the Tau homeworld just as they were planning to colonize it. Then, the Ethereals show up at the darkest time in the Tau's history, to pull them out of a self-destructive spiral. Then, the Tau just happen to find a crashed ship on their planet's moon, when they really need the technology to travel faster than light. And of course, the tiny Warp signature of Tau souls keeps them from being a tempting target for the Daemons of the Warp.
 * For this to be true, Tau would have to be extremely old; yet they've only become a player on the galactic stage very recently and are commonly thought of as a young and naive race. Possibly, modern Tau grew from spores that had remained dormant for thousands of years (Orks, another Old One creation, also grow from spores), but were recently activated by some event or condition. These spores could have been spread throughout the galaxy, seeding many planets. The Tau spores on Earth activated in the second millennium. They were known as Smurfs.
 * Or some of the Old Ones survived the War in Heaven and did not make the Tau until recently. They would not be the only race that survived the war. But this begs the question of what the Old Ones have been doing between then and now.
 * Maybe they fled the Galaxy and are only now returning. Or maybe some ran into the Warp (or got trapped in a warp storm) millions of years ago, and didn't emerge until millions of years later, but to them, only a few seconds passed.
 * Which is why the theory that the Eldar created the Tau makes much more sense. Also note that 6,000 years ago, the Eldar stole a Q'Orl Swarmqueen, which they very likely used as a template for the Ethereals.
 * It doesn't make a lot of sense. The Eldar do all their stuff with warp powers, the Tau have no warp powers at all. The Eldar have a fluid society, the Tau have a strict caste system. Also, unlike the Old Ones, Eldar don't do stuff just because they can. If they made the Tau it would be for a reason, something that benefits them. Making ANOTHER rival culture that can and has killed thousands of Eldar seems very out of character.
 * Perhaps badly wounded Old Ones could survive in a kind of healing trance? This troper hasn't personally seen any fluff to contradict this, so it's entirely possible that the Tau were the result of the last of the Old Ones (maybe Tepok; their lack of warp presence links quite well with his WH Fantasy antimagic approach) waking up, noting how severely screwed the galaxy was, and opting to do something about it.

The Tau are the Necrontyr.
Try putting an (old) Necron Lord and Tau Ethereal model next to one another. Notice anything funny? Other than the one is a skinny metal facsimile of the other? The Tau have the same low warp signature that endeared the Necrontyr to the C'tan, and are clearly protected by some powerful patron. This could easily overlap with the above if they were recreated by the Old Ones for some devious purpose.
 * Both races are known for proficiency with technology.
 * The Necrontyr fought against the Old Ones as they were jealous of long lifespans. And do you know what the average lifespan of a Tau is? 40.
 * In the pre-"Hey, these Tau aren't GRIMDARK enough, let's make them ruthless bastards!" phase, the main difference was that Tau wanted to leave a legacy, Necrontyr just wanted to hurt people who lived longer than them.
 * Even in the new, more cynical version (which still isn't nearly as evil as a lot of players make them out to be) the goals of the Tau remain fundamentally idealistic, so this theory may still have some relevance.
 * Alternatively, the Tau are only a similar race to the one that made so useful servants once, and the Deceiver just can't resist.
 * Also, there is only one named Necrontyr in the Necrons codex. His name is filled with hyphens. Just like the Tau's.
 * Warp Storm cuts off the Tau home planet? Stable Time Loop. We know the Warp can do that.

Both The Above Theories About The Tau Are True.
As the Old Ones fought the Necrontyr and their C'tan masters through their engineered races, they had a number of side-projects going. One of these was humanity. The other, the Tau. Meddling with the Necrontyr brain chemistry to make them less competitive and imperialistic yielded small results, and physical alterations designed to increase the average lifespan and allow them to perceive the warp were only marginally more successful. Despairing of ever reforming their nemesis, the Old Ones left the proto-Tau/neo-Necrontyr on a backwater planet for later study, and continued the war.
 * At some point after the onslaught of the Enslavers and the hibernation of the Necrons, the Eldar came across the Tau. They recognised the Necrontyr by their psychic signature (or lack thereof), despite their evolution into Castes and altered physical appearance (no feet, smaller chins etc). Working off the instructions of the Old Ones, at the direction of a surviving Old One, or on their own initiative, they engineered the Ethereal Caste as described in Xenology, relishing the irony of their greatest foe becoming a potential ally, and hoping for the pheromone-effects of the Ethereal to mesh with the altered brain chemistry of the Tau, preventing the rise of another race of Omnicidal Maniacs. It worked.
 * Again, what do the Eldar get out of creating another rival race?
 * The only notable exception to this success has been Commander Farsight. Losing his Ethereal was bad enough, but not enough to result in rebellion or regression. Stumbling upon a Necron tomb rendered extinct by continental shift was. Recovering a number of artifacts, including the Dawn Blade, (the remnant of a long-devoured C'tan) a heavily coloured degree of the truth about the origins of the Tau was revealed to Farsight by crude communication with his battlesuit's A.I. Enraged by the "unwarranted puppetry" of the elder races, and the Ethereals in particular, Farsight rebelled to reclaim his race's glorious destiny, taking the Greater Good in an entirely different direction. It is unknown how he has acheived such longevity, but one Eldar Farseer claims that the C'tan the Dawn Blade was part of has found an escape route from the clutches of the Outsider - through Farsight.

The Tau Are A Chaos Breed.
Okay, Warpstorms up for most of Tau History. As T'au orbits its sun, it gets closer and further away from the storm. Now, Evolution is essentially change, and who, famously, is the Lord of Change? Tzeentch. yes thats, right, I'm hypothesizing that one of the Dark Powers had a hand in the Tau's evolution. Now, whenever either Tzeentch (or one of his servants) have enough reach from the Warpstorm, He/She/It causes rapid acceleration of the Tau's evolutionary process, thus the times of rapid change. It ALSO allows for an explanation of why the Mont'Au occurred. Khorne was trying to muscle in on the action, so to speak. Tzeench is of course, going to have none of this, so he brings about the Ethereals of Fio'Taun. No more infighting. and to top it off, he made them Blunt, so no more Chaos influence. Alternatively, no Khornate influence whatsoever, the periods of 'hyper-evolution' /were/ screwing with the Tau race, and the Blunt-ness is simply a result of evolution preventing the death of the Tau Race via aforementioned birth defects caused by the accelerated evolution instigated by the Chaos forces of Change.

The Tau Were Created By The Necrons.
To serve as sentient cattle (it may not be coincidence that the Tau are said to be descended from grazing herd animals). They have had impossibly good luck during their development, implying that somebody has been pulling the strings to ensure the survival and propagation of the Tau against the many threats that they are faced with. The Tau are a completely Warp-insensitive race, making them excellent victims for the Warp-averse C'tan and their Necron minions. By ensuring the rise of the Tau Empire, the Necrons have been setting up fodder for their return so that this time there will be less of a chance of them running out of victims. And if conflict between the Tau and their enemies ends up going poorly for the more Warp-savvy races, that's just the icing on the sentient, screaming, doomed cake.

Two Space Marine Legions were too cowardly to fight in the Horus Heresy.
The background mentions several Legions of Space Marines, some who rebelled and tried to kill the Emperor and enslave Earth, some who remained loyal. But it also mentions two Legions whose entire existence has been stricken from Imperial records. They could hardly have behaved any worse than the rebel Legions, so why were their records erased? The answer is obvious if one remembers that "Legion" is a Roman term, and that some Roman Legions had their details hammered out of monuments in punishment for cowardice. Obviously, the equivalent happened during the Horus Heresy.
 * The REAL reason those two Primarchs are unknown is that Of course, this is a WMG page, so where's the fun in actual cold, hard facts?
 * Maybe its less that they are cowardly and more that they are stuck in some bizarre warp phenomena and simply haven't arrived to help yet. I can just picture the shock on people's faces when a Space Marine battle fleet arrives at Sol of the 41st millennium, crying out a warning to the Emperor about Horus' treachery.
 * ...Except that there's already a category for chapters "lost in the warp". Sure, it's not a particularly dignified way for a founding legion to go, but it's hardly more shameful that, say, trying to kill the Emperor.
 * Bah, still a fun theory to think and talk about. And its still valid unless Games Workshop says otherwise (possibly even then).
 * My personal theory is that they rebelled but admitted they were wrong and said sorry. their "Reward" for this was to have their actions deleted, their names forgotten rather than being forever held as traitors and cursed.
 * If you listen to /tg/ the two lost Primarchs are Samus Aran and Stalin.
 * You forget the ANGRY MARINES.
 * Angry Marines are loyalist World Eaters.
 * Does that mean Pretty Marines are loyalist Emperor's Children?
 * /tg/ hasn't decided yet, I think, but that's one of the possibilities.
 * What about the Disco Marines? Surely Slanneshi Noise Marines got their weapons from somewhere!
 * The Scary Marines just scream of being loyalist Night Lords.
 * It could be possible that they were unable to fight during the Heresy because they were busy dealing with the filthy xenos, who always press upon the borders of the Imperium and corrupt the wayward human. After all, the Imperium is pretty freaking huge, even then...
 * Conversely, something awful happened to the 2 missing legions BEFORE the Horus Heresy that had little to do with Chaos...
 * I kind of assumed that the two missing Primarchs got screwed over while being cast into the Warp as infants. I mean, Sanguinus grew wings--it's not too far-fetched to assume two got so badly mutated they couldn't serve as sources of gene-seed any more.
 * But if they were so warped that there gene-seed couldn't be used anymore, why were the legions founded?
 * The Emperor didn't necessarily know this had happened - he may be for all intents and purposes a Physical God, but he has limits. (I think.) The Dusk Raiders were active before Mortarion was found and renamed them the Death Guard; the Dark Angels found Lion el'Jonson back when they were simply the First Legion. If the Emperor predicted he'd find them, but not that they were seriously mutated, he could found a legion, then quietly disperse it and find some secret job for the survivors.
 * Such as becoming the Adaptus Custodes and the Grey Knights? Just a thought.....
 * Alternate Character Interpretation - The two missing Legiomns weren't afraid to fight, but they alone understood the full consequences of the Heresy. They refused to fight in the hopes that they could be around afterwards to clean up the mess, or to set a good example to those who weren't as smart as them. It all backfired horribly when they were excommunicated and/or executed/banished for cowardice and treason. Sapce marines, after all, are war machines built and bred to fight in some way or another - what could be more shameful and deserving of ignonimity than refusing to fight AT ALL?
 * A fairly recent short story, The Lightning Tower implies that the two missing Primarchs disappeared before the heresy. There were statues of the Primarchs in the palace of Terra and two of them were missing from their place. Not only that, but an early story has Horus TIME TRAVEL thanks to the warp and find the twenty Primarchs in the emperors lab, before they were taken by the warp. He saw the two unknowns and commented on "Lost Potential"
 * Following that, the two missing Primarchs and their legions may have destroyed each other in a mini-heresy.
 * The two legion fleets were flying together in a joint operation commanded by the emperor, a message was sent ordering a fleet maneouver but by mishap one of the legions recieved a garbled message with the orders reversed. Consequently the two fleets entered a collision course with neither fleet willing to disobey a direct order from the emperor they plow into each other and both are wiped out completley. The other legions forever remember their gallant bravery but never mention their blind stupid obediance.
 * Alternately, they were wiped out by xenos/Chaos before the Heresy.
 * No, one of them is Gazghkull, Prophet of the Waaaargh!, who was somehow transformed into a long dormant Ork spore. Thiss is why he is the biggest o' all da Orkz!
 * No, the 2 missing Primarchs are never named and the records are deleted because their names where actually Gork and Mork, and where involved in a time travel accident that send them and their legions at the time of the War in Heaven.

The Alpha Legion Primarch Alpharius is not dead.
Who is said to have killed Alpharius? The Ultramarines, the proudest Chapter of Space Marines in the Imperium. And what would be a prouder achievement than having killed a rogue Primarch? Also, Alpharius was a Magnificent Bastard, so the Ultramarines could have killed a clone, a robot, a hologram.... That way, Alpharius could control the Alpha Legion without anyone trying to kill him. This would perfectly fit with the Alpha Legion's record of convoluted strategies, and would explain why the Alpha Legion weren't terribly distressed about the "death" of their Primarch.
 * "Just as planned."
 * If you read Legion, . So you're more correct than you might think.
 * Wait, Alpharius is a Primarch, so saying he has a twin means that Omegon must a) be a Primarch too and b) be one of the 2 missing Primarchs!!
 * Yes he's a Primarch, no he's not a missing Primarch.  It is possible that the Emperor himself never found out about this.
 * It's assumed he is composed of two seperate bodies, in reality he may have even more, or perhaps he exists in all those in his legion as some sort of geneseed fluke.
 * Another incredibly wild guess. Cypher, is actually Alpharius/Omegon in disguise. What? I sure as hell wouldn't put it past him.
 * It would explain his almost God-like ability to stir up trouble and then escape unharmed.
 * ...but not his connection with the Dark Angels.
 * Easy. Alpharius killed the real Cypher, who was a Dark Angel. Now he's just masquarading as him.
 * Doesn't work. There has been several sets of rules for Cypher, and none of them had the stats to indicate he was anything more than a skilled Space Marine, let alone a Primarch. Or the points cost. However, this Troper believes that Alpharius/Omegon merely pulled their "we are all Alpharius" trick and fooled the Smurfs into killing a normal Alpha Legionnaire. It wouldn't be the first time their charade had fooled fellow Space Marines...which means that both Primarchs are still out there.
 * Space Marines, maybe, but Guilliman was a primarch.
 * Plus the rules make it clear: Cypher cannot die, not until his mysterious benefactor is done with him.

The Tau are engineered by the Eldar
As shown by Xenology, the pheromone gland in a Q'orl and a Tau Ethereal are identical, and a Q'orl legend laments the loss of one of their queens at the hands of the Eldar. Q'orl queens also control their subjects through pheromones. Coincidences are not helpful.
 * If the primary Eldar goal is to keep as many of their kind alive no matter how many members of other races get screwed over, wouldn't they have used the Tau as a slave race (or, on a good day, an "indentured race") rather than plonking them on the Eastern Fringe and waiting for them to build their own guns and begin battling everyone, including the Eldar?
 * Maybe that was the plan, but they fucked up.
 * This is the ELDAR we're talking about. They see the future. They may fuck up a fair bit, but to miss the emergance of a rival empire from their own manipulations? Unlikely. Plus if they wanted a slave race for something, they would have done it a long time ago.
 * I think you are seriously overestimating the Eldar's capacity to not fuck things up.
 * It's the Dark Eldar who really fuck up, the Eldar tend to come out OK.
 * That's the whole point. The Eldar are training the Tau. Battles between the Tau and the Eldar are either training, unfortunate misunderstandings, or legitimate conflicts of interest. The only way for their creations to become effective powers that might turn the galaxy around is to face, survive, and defeat all threats.
 * Sacrificing thousands of their own people to help someone else? Doesn't sound like the Eldar to me. If they were going to create effective powers they would have plonked them a long way away from any Craftworld. And probably mindfucked them into complete loyalty. And destroyed them when if that didn't work.
 * Or the Eldar created the Tau do do what they could not. There are many theories that the Tau were created to destroy Chaos, since the Eldar cannot.The Tau even have many upgrades that prove this: the apparent lack of soul (nothing to strengthen Chaos), Lack of Psycic presence (immunity to possession from demons), and incredible technical innovation (to fight demons and adapt to the ever-shifting powers of Chaos). The Eldar may have made the Tau so they could get their homeworlds back.
 * The Eldar are willing to sacrifice billions of other species to save thousands of Eldar, and redoubtably willing to sacrifice thousands of Eldar to save the entire Eldar species. Perhaps the tau are part of a very, very long game.
 * There is a theory that the Eldar DID create the Tau, but didn't know about The Outsider - another C'Tan who may or may not be sleeping under the surface of the Tau planet.

The Tau is Krikkit.
Really, cut off from the rest of the galaxy, only to find a crashed spaceship and become uncannilly proficient with technology in a short time and go on a rampage.

Alternatively they are the Yehat.
 * You can't get Yehat.
 * Alternatively alternatively, the Tau are an evolved form of the Qunari.

Cegorach is the DM of Warhammer 40k

 * The setting is run by a sadistic god of dirty tricks. How else do you explain it?

The Emperor's stasis on the Golden Throne is part of a 10000-year Xanatos Gambit.
It's got something to do with Neon Genesis Evangelion. Blame Matt Coates and his The Final Crusade NGE-Warhammer40k crossover for the odd idea.

The Warhammer 40k Universe is part of the Marvel Multiverse.
And, as such, various elements from 616 are localized appropriately:
 * One word: Adamantium.
 * The Hulk becomes da Orkz. Please, don't make them Waaagh. You won't like them when they Waaagh.
 * Super Soldier Serum + Tony Stark's armor and weapons = Space Marines.
 * Alternatively, Fio'O To'ni St'ark was one of the finest minds of the Tau Earth Caste. Abducted by a radical Inquisitor's retinue and forced to recreate Tau technology for them, he instead built Powered Armor and used it to escape captivity. Voila! The Battlesuits were born.
 * ...In a CAVE!! From a box of SCRAPS!!!!!
 * Professor Xavier is a crippled old man who sits in a chair all day and uses a combination of his immense psychic powers and a powerful machine array to communicate with and guide people all around the Universe. Replace Cerebro with the Astronomicon and you've got the God Emperor of Mankind.
 * The all-devouring Tyranids are Galactus.
 * No, no, the Tyranids are the Annihilation Wave. Galactus is another C'Tan.
 * Excuse me, Gah Lak Tus. (Ultimate version, who are a kind of scuttling skull-bug cyborg race).
 * The Devourer certainly sounds like a C'Tan.
 * Human/Mutant relations is a popular subject for various multiverse stories: Age of Apocalypse, House of M, etc. In the Warhammer 40k universe, they're more strained than usual.
 * And finally, Warhammer 40k takes place in the universe designated Earth 40,000. As it should.
 * A question: Who's Deadpool-40,000?
 * Let's see. Who in Warhammer 40k is bugfuck insane, hilarilously awesome, and Chaotic Neutral? Da Orks. When Waaagh!Dedpool gets going, the galaxy will burn. Then he'll move on to whatever the Nids are running from.
 * ... I may just have to get an Ork army.
 * Is no one going to mention the fact that the Marvel universe now has a huge rift in it? Through which lots of eldritch abominations are coming? Of course there could be a simpler explanation...

The Emperor and Tzeentch used to be one.
The Emperor, before Slaanesh showed up, is said to have been pulling strings of humanity for thousands of years, so he ought to be able to avoid What An Idiot moments he had after he became Emperor. Obviously, the part of him that was the sneaky bastard is somewhere else, essentially pulling another Xanatos Gambit i.e. Tzeentch. Slaanesh, Khorne and Nurgle aren't the brightest bunch, so they probably didn't notice yet.
 * Alternately, the Emperor might still * be* Tzeentch, no splitting of his aspects, just millennia of living a double life within the warp. Those Imperial Unwitting Pawns never noticed a thing.
 * What is the Emperor? A Magnificent Bastard. And what did he plan to bring to Humanity? Hope and change. Who is Tzeentch? The God of Hope, Change and Magnificent Bastardry. Just. As. Planned.
 * Slannesh's creation predates the Emperor (and indeed mankind) by millions of years.
 * No, it doesn't. Slaanesh's birth actually caused the Age of Strife and humanity was a space-faring species by then.
 * So you're saying the greatest leader humanity has ever known is the embodiment of hope and change? Does This Remind You Of Anything?

Tzeentch is one of the Eldar's greatest allies
Whilst Tzeentch is a Chaos God, his 'fellows' are by no means outside the reach of his scheming. To which end, had Tzeentch learned of the Eldar's ultimate plan (which would weaken or kill Slaanesh, and free the Dark Eldar from his control), he may well be keeping the other forces of Chaos focused on fighting the Imperium so as to allow the Eldar to eliminate one of his primary rivals. The alliance is also how the Eldar acquired Tzeentch's lessons in Manipulative Bastardry 101.

It's another of Shinji's dreams (Warhammer 40000 edition)

 * God Emperor of Mankind = Shinji
 * Primarchs = Shinji's personality traits
 * Tzeentch = Gendo/SEELE
 * Slaanesh = Misato
 * Khorne = Asuka
 * Nurgle = Rei/The Sea of L.C.L.
 * C'Tan = The Angels
 * Gork & Mork = Asuka
 * Shinji is clearly The Emperor, Tzeentch and both Gork and Mork. Rei is a Primarch, Asuka is Slaanesh and Khorne, Kensuke is the Omnisiah, Touji is the Lord Commander Militant of the Imperial Guard, Misto, Gendo and Ritsuko are the heads of the Inqusition. For more, see Charles Bhepin's Shinji and Warhammer 40k
 * Shinji is Chaos W40K Undivided, as he's got all the factions running around in his skull. Apocalypse Rei is obviously Gork and Mork ("waaagh."). Asuka has Khorne's aggression and Slaanesh's pride, and both are struggling with the Greater Good ideology for dominance, but there may be the potential for a Primarch somewhere in all that confusion.

The claim that the explosive in bolter shells is "depleted deuterium" is a lie spread by the Adeptus Mechanicus.
Deuterium is a radioactively stable isotope of hydrogen, so "depleted deuterium" is both physically impossible and a terrible idea for the main payload of an explosive shell. The fact that bolter rounds work, and work well, suggests that the Mechanicus are aware that Elements Do Not Work That Way. Thus, any reference to "depleted deuterium warheads" in the WH40k fluff is a load of technical-sounding gobbledygook intentionally spread by the Cult Mechanicus to prevent anyone from recreating this sacred and revered technology without their blessing. The true payload of a bolter shell is a secret known only to the Tech-Priests -- and they aren't telling.
 * The same is also true of any references to bolter shells as "caseless ammunition", as suggested by the rather prominent cartridge-ejection slot on the side of the Astartes Mk Vb boltgun. Granted, earlier boltgun models seem to lack this cartridge-ejection slot, so it's possible that some bolter shells are caseless, but claims that this is a universal rule are (possibly intentionally) fallacious.
 * The background material seems unable to decide. Bolters are often called caseless, but the detailed description of a boltgun in one of te Imperial armour books mentions it having a case. There being several variants, some of which use a case and some of which don't seems likely, especially since boltgun shells are essentially miniature rocket propelled grenades and don't necessarily need a case (altho having one would probably reduce a chanse of it exploding prematurely).
 * This is true, Dark Heresy mentions that they are "Marine" Bolters and "Human" bolters the human ones are smaller and have cases because Marine bolters are too heavy and recoil would break a human's arm off.
 * Also, bolt rounds are likely two-stage to avoid the crappy short-range velocity of Real Life rocket ammo. This doesn't strictly require a case, but the engineering is easier that way.
 * Despite being physically impossible and a terrible idea, it actually works anyway, because of the majesty and benevolence of the Omnissiah.
 * You mean the Void Dragon...
 * Caseless doesn't refer to the shells themselves, but their packaging. They're caseless because they come in plastic bags.
 * Don't be silly; they come on plastic sprues in little cardboard boxes.
 * The Tau and Eldar could probably reverse engineer them over breakfast, and have found their weapons better. And...for some reason no one in the Imperium is smart enough to do it.
 * The only time any Eldar or Tau cold get their hands on Bolter ammo is if its being fired at them. Not only that, but Eldar have to much disdain for human tech to use it and Tau don't like non-plasma weapons very much.
 * Since Promethium is real-life element that has has its name applied to a completely unrelated material in the WH40K universe, it's possible that the name Deuterium has likewise been misapplied by the Adeptus Mechanicus. Just because they recover old information doesn't always mean they know what it means or interpret it correctly; they could have a partial list of names but not know which substances they refered to in ancient times, so they simly use what sounds cool for each material they rediscover. Prometheus is associated with fire, so call a flammable fuel Promethium. Deuterium, according to scraps of ancient literature, has something to do with nuclear reactions or the sun, so call a high-powered explosive Deuterium. Remember, they've got 40,0000 plus years of Memetic Mutation to deal with.

The Tau were engineered by the Emperor to bring humanity back in line.
They were discovered by humanity during their stone age but are miraculously saved by a warp storm and then turn up a few millennia later with technology surpassing the Imperium. Their origin stories are similar (fractured species stuck in endless civil wars until unified by mystics: The Emperor for the humans and the Ethereals for the Tau). They are incorruptible by Chaos (no warp presence) and are known to have easily convinced some less fanatical human leaders to defect to their empire. By the time the humans (and, by extension, the Emperor) first discovered them, the Imperium was already in a state of decay thanks to corruption, bureaucracy and blind fanaticism, so the Emperor may have decided to save the Tau so he could repeat the process with them while avoiding the mistakes he made with the Imperium (a whole caste of rulers instead of a single god, a rigorous caste system to prevent another Horus Heresy etc.). His ultimate plan is to have the Tau conquer the Imperium, resurrect himself with Tau technology and then conquer the entire universe with both races.
 * Combining this with the "Ethereal refusal" version of the Eldar theory...the Emperor had most of the work done for him. He just needed to keep a natural warp storm going for a few millennia, and make it "accidentally" destroy the Webway connections. The result? Instead of a psy-resistant and technologically advanced puppet race for the Eldar, an independent Tau empire who would either conquer and reform the corrupted Imperium or challenge it out of its rut.

Mammy Yokum's tonic, seen in the musical based on the comic strip Li'l Abner, was one of the ingredients used by the Emperor to create the first Space Marines.
Men who take the tonic undergo massive physical development, but completely lose their sex drive -- a perfect combination for the superhuman warrior monks of the Legio Astartes. The tonic's made from berries that only grow on a tree in the Yokums' yard, so sometime before the start of the Great Crusade, the Emperor must have been to Dogpatch and harvested some of those berries. In fact, if he was also Jubiliation T. Cornpone sometime between his stints as Jesus and Akihiko Sanada, it's possible he planted the tree himself so he could harvest from it later.

The various source-books and other materials dripping with GRIMDARK are anti-Imperial propaganda.
Almost every sourcebook in the game presents its subject as a terrible, nigh-unstoppable foe of the Imperium who will surely doom its last futile struggles. Yet the literature-especially the accounts of Ciaphas Cain and Ibram Gaunt- often demonstrates the courage and professionalism of the Imperial Guard at its best and often and portrays the Imperium and the Imperial Faith in a much more positive light. Clearly, the doomsday predictions and extreme dystopian elements of the various sourcebooks are either anti-Imperial propaganda or only apply to the Imperium in broad generalities.
 * "Thought for the Day: It is better for a man to be afraid than happy." The various source-books and other materials dripping with GRIMDARK are Imperial propaganda. The Imperium is a loose empire that spans the entire galaxy. It can take months for messages to get back and forth to some of the more isolated worlds, and even longer to bring forces to bear on any particular point. The only thing keeping most systems from declaring independence from this soul-crushingly oppressive regime is the knowledge that (allegedly) there are a thousand nameless horrors waiting just out of sight to tear them to pieces, and it is only the inexhaustible might of the Imperium as a whole that has a chance of protecting them. The eternal "war-footing" is also useful as an excuse for the atrocities the Imperium regularly commits on its citizens, brings in the annual planetary tithes, and keeps Imperial Guard recruitment figures high. This is Nineteen Eighty-Four Recycled in Space.
 * But why would they claim they commited EVEN MORE atrocities then they already do? I mean, every evidence out there suggests there's only one not-100%-crap alternative to the Imperium already, so why make yourselves look worse?
 * Accurate information about aliens is ruthlessly surpressed by the Imperium for reasons of ideological purity and because alien or chaos-worshipping cults aren't uncommon. The Imperium constantly tells it's citizens that not only is every single alien personally out to get them (while keeping actual information at a minimum) but keeps them in a constant state of terror to keep them in line.
 * "Wow, if our guys have to blow up planets rather than let our terrifying soul-devouring enemies get a hold of them, it must be dangerous out there.''
 * What's the most-played army, the one most players start with? SpaceMarines. Most of the GRIMDARK fluff isn't general Imp propaganda, it's Astartes indoctrination, aimed squarely at their sense of superiority to the rest of the Emperor's servants and their fatalistic attitude. The rest is likely by and for Inquisitors, who aren't known for their lack of paranoia.
 * There's no inherent contradiction. The Imperial Guard really are professional, competent, even heroically badass soldiers. They just can't do much against the Cosmic Horrors, space dinosaurs and assorted demigods except act as cannon fodder. The Imperial Faith is at one and the same time a comfort and inspiration to humanity and an excuse/rationale for its worst excesses (true of many real faiths). The Imperium is both a fascistic nightmare of Orwellian conformity and the only real chance we've got. In addition, it spans vast amounts of worlds, easily enough to cover everything from forge worlds to remote agri-colonies.

== Alternatively, the stories of Ciaphas Cain and Ibram Gaunt are Imperial propaganda designed to overplay the power and competency of the Imperial Guard and the relative happiness of the Imperium. == These individuals' characters and experiences contrast abruptly with the dystopian view of the Imperium at large. If the dystopia is true, then these individuals, as well as other heroic sorts with relatively endearing morals and behavior, must be entirely fictitious creations, possibly published by the Inquisition or by the Imperial Guard itself.
 * Ciaphas Cain's adventures are explicitly published by the Inquisition.
 * But only to the Inquisition. Why would the Inquisition produce propaganda for the most knowledgable agents of the entire Imperium?
 * Cain's alleged exploits and biography are strongly backed by the Imperium as a great propaganda tool. Cain's actual biography is published by the Inquisition for its own use: as a form of education, information, and of course, entertainment.
 * So, we're agreed. The Ciaphas Cain novels are the only accurate information about Warhammer 40k.
 * Unfortunately, Ciaphas Cain is considered an Unreliable Narrator.

Tzeentch is planning to make the universe less GRIMDARK.
What is the great schemer lord of magnificent bastards? The god of HOPE. If people lose hope he starves, thus he realizes the world is too GRIMDARK for him to truly prosper so he works his plots to make the universe more gray since a bright and happy universe does not create maximum hope either. A gray universe were a bright future is always just out of reach however is perfect. His pawns for this? The Tau of course, their idealism and knight templar status are perfect for a seemingly bright but gray universe.
 * He's not exactly doing a good job, is he...
 * Which is what he wants you to think...
 * I'd actually say he's doing a perfect job. Legend fades to myth and is forgotten. Let's look at the Imperium. Empy raises humanity to amazing levels pre-heresy. Hilarity Ensues. Humanity declines, but remembers the past, and hopes to reclaim its past. Rinse and repeat. He basically made a stock market using humanity as a base.

Tzeentch is actually the good guy from the franchise.
He will eventually reveal (or more likely just play the final part of) his great plot of backstabbing all the other gods, (that are just doing his bidding anyway) turning the grimdark galaxy into a rather prosperous and possitive place. He is the god of change; and the greatest change you can bring to the 40k universe is turning it into a realm of progress and peace. All the horrors and blue fire and howling terrors might just be a masquerade to the fact that he is about all the contrary, and uses it to cover up the greatest hiden plot of the galaxy. Anything big that might happen in the future, from pretty much any faction would empower him, for he is the god of change. The emperor dying, the necrons waking, the tyrannid's boogie man arriving, all that is just Change lurking and could be enough to empower Tzeentch into reaching previously unknown levels, power he will use to bring; guess what. Hope and Change to the Warhammer 40,000 Universe.

Enough Dakka can only be achieved by turning everything that isn't Dakka into Dakka.
So, essentially, do to the Universe what the Tyranids are planning, but only with Dakka.
 * Nah, youse got ter ave enuff bitz left ter nail all der shooty bitz to, and den youse got ter paint it all red.
 * But if you turn the entire universe into a gun that shoots itself, what's left to shoot at? This may be the greatest only Orkish philosophical paradox of all time.
 * Itself. It isn't Orky enough.
 * No, no, no, You're Doing It Wrong! Enough Dakka has already been achieved: It's called Chouginga Gurren-Lagann's Maelstrom Cannon. A weapon that can hit every point in time and space is pretty much Max Dakka.
 * Can it hit parallel dimensions?
 * Got me there...
 * Well, as long as Rossiu is in the other dimension for targeting purposes...
 * Hittin fings aint der point of yer shoota, it's dere to make loads o noise while you get all close up an proper like a real Ork.
 * Alright... here's my take on 'enuff Dakka': You must create a weapon that can hit every point in space and time in the multiverse... with bullets that are each composed of every point in space and time in the multiverse... at point blank range to every point in space and time in the multiverse... And to clarify, the term "multiverse" includes: all alternate realities, parallel realities, perpendicular realities, potential realities, imagined realities, unimagined realities, inconceivable realities, and impossible realities. So you need a gun that shoots at everything, with everything, when next to everything. Now... how can we achieve * dramatic chord* too much dakka?
 * So the Crisis on Infinite Earths was the result of the Anti-Monitor trying to get together enough Dakka?
 * That would only be enough dakka if the weapon can hit every point in the multiverse WITH every point in the multiverse, at every point in time in the multiverse, infinity times per 10^-infinity seconds. Remember, one of the key points of dakka is rapid-fire capability. Hitting everything once isn't orky enough.
 * You've achieved Too Much Dakka if yer shoota has so many barrels and gubbinz and whotnots stuck on it yer can't pull da bloody trigga.
 * As any Big Mek would say, "Stikk on anuvver trigga, den shoot evryfing wot moves!"
 * Let me repeat this to make it absolutely clear. You can never, ever have too much dakka.
 * Gork an' Mork. Dey gots Enuff Dakka. Me gonna choppa and dakka more squishy mans an' bugs an' things until me bigs enuff. Den me gonna smash Gork an' Mork an' take deir Dakka sos me can have ALL DA DAKKA!
 * Naow Add one mo' dakka. And one mo'. And one mo...
 * I would just like to point out that there is no way (physical or meta-physical) to achieve ENOUGH Dakka. Looking for too much Dakka is just being silly.
 * The only way to get enough Dakka would be to turn everything that exists in every form of reality into a gun that fires everything that exists in every form of existance and those reality bullets fire more reality bullets causing an infinite loop of dakka. If that still isn't enough, the gun fires everything that does exist in any form of reality and everything that DOESN'T. Of course, everything is rocket propelled and rapid-fire while on fire and covered in pointy death.
 * Make it an auto shotgun and that's about halfway there.
 * You have enough dakka when your opponent falls asleep during your shooting phase.
 * You hummiez gots it all wrong! Youz are muckin about gobbin bout dakka. DA ORKS IS MADE FOR FIGHTIN!

Enough Dakka will be achieved if the totality of existence is destroyed.
If there's enough to shoot at, no dakka is necessary, therefore, any amount of dakka is enough, even none.
 * DAKKA IZ ALWEYZ NESSASSARY
 * DAT AINT ORKY, IM GONNA CRUMP DIS GROT LOVA- er, I mean, what? How is it even dakka if you aren't shooting? You iz muckin' about!

Coversely, if an Ork is ever convinced he has enough Dakka, the universe will end.
Since Ork technology works because they think it does, and Orks can never have enough dakka, simply convincing an Ork that he does have enough Dakka will turn whatever he is holding at that time into the most potent weapon in the universe.
 * Correction: it's the result of the low level psychic powers that manifest in all Orkz and Humans. Miracles occur through faith (billions of souls SAY she can do it, so she can), and thusly ork technology works. So, if enough orkz could be organized under a being who knows this (say, their creators, can't remember if it was the Old Ones, C'tan or Necrontyr), you could arm a billion Orkz with black hole cannons, or, yes, create enough dakka. However so many orkz believe you can't get that, then they can't. Tl;Dr Because billions of orkz KNOW it to be so, the Red'nz do indeed go faster.

Boo is the Emperor
That's why can't reincarnate. He got stuck in a body of a hamster, because of Tzeentch.
 * And Minsc must be one of the Missing Primarchs.

Tengen Toppa Gurren Lagann is the ultimate Orky dream - just with "filfy humies" instead of Orks.
Think about it: The series is pretty much the ultimate invocation of Clap Your Hands If You Believe, where characters do Badass crap because they believe they can. Orks grow larger the more accomplished they become. So should we not expect that a Gargant mecha large enough to throw galaxies around, with a preceding form that has Almost Max Dakka lotsa dakka, just not enuff, is probably the dream of every Mekboy. Unless, of course, they want something large enough to throw everything else in the universe around... Then, again, it seems to be running on Wyrdstuff and if so, even the Mekboyz might not want to mess with such things.
 * Totally not inspired by Gorkken Morkann. Seriously.
 * Red wunz do go fasta, after all.
 * So, WAAAGH! is Spiral Power? I knew it!
 * Yeah, Spiral Energy is powered by hotbloodedness, which means Waaagh!.......

Corresponding to the above theory, Orks are a spiral race.
Sure, they aren't quite like humans, they were created artificially, they don't really understand things like love, and they don't really follow anyone except out of fear and possibly admiration of bigness, but they're green (from algea in thier skin) and WAAAGH! sounds extremely similar to something spiral energy would do. Not only that, almost all of thier enemies are excessively grimdark (unsurprisingly), and they are the least angsty of all the factions.

Warhammer 40000 is All Just a Dream of Horus
As we see at the end of "Horus Rising" he's under a lot of stress, so once he gets to have some sleep, he has a really bad nightmare. His own betrayal in the dream, is actually a symbol of his own fear of not living up to his father's expectations.
 * That's one long, messed up dream.
 * Or, it's a Dream Within a Dream...

The Space Marines were derived from the Brotherhood of Steel
The armor of the Brotherhood of Steel guy in the early Fallout 3 trailer looks suspiciously like the armor of a Space Marine. Obviously, the Emperor created his Space Marines in their image, after living through the nuclear apocalypse and using the Brotherhood to lead mankind back into civilization and the Age of Technology. The Golden Throne probably has a "Vault-Tec" logo stamped on it somewhere.
 * Or he played Fallout and liked the design so much he... ahem... borrowed it.
 * Well, the backround does state the Space Marine power armour is derived from the so-called "Thunder armour", a type of power armour used by the inhabitants of the post-apocalyptic Earth.

Games Workshop is secretly a cult worshipping chainsaws, and Warhammer 40000 is their attempt to subtlely proselytize.
It's not that unbelievable...
 * You lost me when you said "subtlely".
 * Well, they didn't say it was a religion and how much they like chainsaws...

...and they're preparing their followers for an epic battle against the Church of Scientology
The newest Chaos iconography in the 4th Edition Chaos Space Marine codex makes it pretty clear. Come to think of it...Rage, Corruption, Scheming, and Arrogance happen to be the chief vices affiliated with the Church, and the whole operation is certainly rather cult-ish. It seems to be recruiting from the rich and powerful, perhaps to build up a private army? And the whole "thetan" concept includes nonhuman spiritual entities being trapped in mortal flesh...daemons? This would make Xenu either a noble alien warrior who defeated the cult's precursors millennia ago, or else a daemon prince of Malal (which would explain why he and his followers haven't returned to Earth to finish the job, as the Fifth Chaos God is in a major decline). All this evidence combined proves without a shadow of a doubt that one day soon we shall be engulfed in an ultimate showdown involving Tom Cruise, John Travolta, and chainswords.
 * That would trump The Ultimate Showdown of Ultimate Destiny.
 * This is a very worrying thought. What happens to those of us who lead Chaos armmies? Would we be lumped in with Scientologists? Or do we get use their own weapons against them?
 * You get to fight them on behalf of Malal, Suvassin and Necoho depending on your personal preferences.
 * I'll go dust off my Dreadaxe...
 * Don't buy it at all; based on what an army box costs, I'd sooner believe GW -are- Happyologists.

Japan sunk into the Pacific or was otherwise obliterated some time before or during the Dark Age of Technology.
Despite various Imperial Guard Regiments & Space Marine Chapters being influenced by various Earth cultures, pretty much the only Japanese-influenced stuff seems to be Eldar & Tau.
 * Alternatively, they all moved to Mars and became the Adeptus Mechanicus. Well, they do make mecha...
 * One issue of White Dwarf, celebrating a Space Marine Codex, featured Marines with samurai banners and symbols.
 * Considering the level of firepower routinely thrown around in the setting and how geologically unstable Japan is, it's highly unlikely Japan survived the Unification, and odds of Japan surviving the end of the Dark Age of Technolgoy are roughly zero. One well-aimed shot from a lance battery would wipe out most of the nation, much less actual * firepower* being deployed there.
 * Alternatively, Japan underwent a landmass-to-space conversion, and Starslip Crisis is really about the Age of Technology. Obdrath von Lucifuge and the Terran Consortium leaders were servants of Tzeentch, seeking to create even more chaos (little-C chaos, not big-C Chaos) out of the flaws of the starslip engine, but failed. Now it'll all end when the warpstorms arrive. Also, sometime just before the Age of Strife, the Cirbozoids will flee this galaxy for another, only to return eventually as the Tyranids.
 * They get at least one planet, and an off-the-cuff mention that they're still practicing sumo, in Farseer.
 * 1d4Chan accurately describes the Imperium as being: "a nation ruled by a Divine Emperor with legions of fanatical warriors who believe that glory awaits those who die in battle in his name with officers carrying swords, infantry engaging in fanatical charges, suicide missions considered a proper way to end one's military career, high ranking officers wearing dress uniforms comparable to those from 18th/19th century Europe, and their most powerful weapons are gigantic humanoid mecha." If anything, Japan became the dominant culture.
 * This doesn't affect planets settled back before Old Night, but it seems none of the Earth cultures we know made it through the Age of Strife intact. Every Terran we see in the Horus Heresy series seems to come from a mix of multiple present cultures and ones yet to develop.

Farsight is working with/secretly being controlled by/been replaced by/really likes the Necrons/Eldar/Squats/Skiiiiiinks iiiiiin spaaaaaaace!.
Even Games Workshop loves messing with us on this one. http://www.games-workshop.com.au/games/40k/tau/painting/farsight/default.htm

The Chaos Gods plan is to make the Emperor another Warp diety.
The Chaos Gods, if they ever win, will destroy themselves. So, obviously, they need something or somebody to stop them from winning. So, why not create a diety that would oppose them? And who's better than a person, who already has a cult and already is a danger to them?

6th Edition will either never arrive, contain mechanical changes only, or reboot the canon.
This one seems pretty obvious, but just how the heck is GW gonna top the GRIMDARK-titude of 5th? Since things obviously can't get any BETTER, either the canon is gonna continue exploring the monumental screwedness of the universe at large, or GW is going to say "Alright, we can't think of a way to make this any worse. We're starting over."
 * 6th Edition will be the End of the World Special. Those naive Tau will have their hopes crushed by Tyranids, Orks, and xenophobes. The C'Tan on Mars will wake up. The Eldar craftworlds will become silent tombs drifting through the void. Abaddon will finally, finally win a campaign. And everywhere, humans will be dying in droves as the tide of unspeakable horrors plaguing the galaxy utterly extinguishes the Imperium like the tide washing over a candle. The narrative campaigns players take part in will not determine if the "good guys" live or die, but how they die - more specifically, how long humanity lingers before succumbing to its inevitable fate. On the one hand, we'll get to play out the Final Siege of the Imperial Palace. On the other hand, one helluva Downer Ending. Afterwards, the game will only continue as "historical reenactments" with occasional rules tweaks and new models, for if a 7th Edition is attempted to advance the plot, a black hole will swallow the Earth.
 * Or CIAPHAS CAIN, HERO OF THE IMPERIUM will come back, complete with an in game unit. Therefore, saving humanity.
 * But as of the publication of the Cain Archive, he's been dead and buried with full military honors for a number of years (while still on the official payroll). So how could he...oh, duh, Cain must be Jesus. And, therefore, also God/The Emperor.
 * Cain's books are written as of M42.100. The setting is currently at late M41.999. So he's alive in-setting, and book five is about his action in the 13th Black Crusade.
 * Or Kharn the Betrayer will find Cain and make sushi out of him, because everybody wouldn't SHUT UP ABOUT HIM and so Kharn felt he had to challenge him.
 * Aw, Kharn wouldn't do that, he's actually a pretty nice guy.
 * On the other hand, all the surviving Primarchs will return, the Tau will reach a technological singularity, the Eldar god of the dead will awaken, and the Starchild will be born. Our reality will be unable to contain the level of awesomeness, and will explode. AND IT WOULD BE AWESOME.
 * There is only one possible way to make 40K even MORE grimdark, and that's the one where an Eldar craftworld kamikazes into T'au, the Eye of Terror gets 70% bigger overnight, and Tyranid gaunts suddenly have "venom cannon" as their basic weapon.
 * Actually, there is one other way to make 40K even more Grimdark - portray the Imperium as evil. Eliminate all language portraying the Space Marines and Imperial Guard as the Defenders of Humanity. Show records of dozens - hundreds, even - of alien races exterminated by the Imperium. Make a big thing out of how callous the Imperium is towards its subjects. And finally suggest that an Imperial victory would result in the extinction of all other alien species and a permanent dark age for the human race.
 * And that's different from the current portrayal how?
 * A few possibly modifications:
 * A new Founding is attempted, but something goes horribly wrong. Every single chapter created is mutated, and all resulting marines are either wiped out, or flee, possibly forming a new faction of mutants or joining Chaos. The Imperium has lost its ability to create new Space Marine chapters.
 * Several planets in the Segmentum Solar turn out to be Necron Tomb Worlds. One of these is Mercury. The Mercurian Necrons make landfall on Earth, but are defeated by the combined forces of the Imperial Fists and the Adeptus Mechanicus. The Adeptus Mechanicus receive a codex.
 * Yet another way to make the setting even more GRIMDARK: The arrival of whatever the Tyranids are running from.

The Kroot are a form of Tyranid used to gather DNA for when the Tyranids finally come and kill everything.
The Kroot consume the flesh of dead enemies to take useful traits from them. The Tyranids also take on traits of defeated enemies. It wouldn't be a stretch to assume that the Kroot are being used by the Tyranids to get whatever useful traits they can before the final invasion get so that the Tyranids have an easier time conquering the galaxy, what with all the super soldiers and killer undead robots and space demons and such.
 * It has been mentioned in a story that the Kroot are expressly forbidden from eating the flesh of Tyranids by their Shapers, ostensibly to avoid creating some sort of monstrous super-predator. Makes you wonder how that particular taboo got hardwired into the Shapers' heads....
 * Isn't it because it would effectively create Kroot genestealers? As in, knowingly loyal to the Tyranids? Kind of like how eating servants of Chaos is also bad for the Kroot.
 * Just wondering, what information is this based on? Not that I'm doubting, but I just wanna see.
 * Well, in Dawn of War: Dark Crusade, the Tau commander is forced to go Imperium of Man on his Kroot allies after the Chaos strongpoint assault...
 * There used to be a relevant article on the offical GW website, but it seems to have disappeared in the revamp. A similar point is brought up in the Ciaphas Cain story For The Emperor.
 * Although in that one, the Kroot spat out Genestealer-tainted flesh.
 * He did freak out when he though some purebreeds were going to 'taint' some of their fallen (too bad no one told him that's not how stealers work)

We're going to see what the Tyranids are running from.
Considering how Grimdark the setting is, the only way we're going get any more Grimdark is by having the effectively unstoppable factions have their own breakdowns (but not in time to save the rest). The Necrons have already started to show theirs, but what about the Tyranids? From information on this Wiki, they're supposedly running from something. If that's the case, what?
 * Gaseous Energy Beings whose bodies are chemically identical to Raid.
 * Everyone thinks it would be somthing bad. What if the Tyranids are running from somthing that is specifically hunting them down to remove their evil?
 * Because that's not how things work in Warhammer 40K and you know it.
 * Because every faction is evil, and would therefore be targeted by something that even the Tyranids are afraid of.
 * What is the one thing that all the races (or at least their leaders) are completely terrified of? The Cosmic Force of Peace and Love! Think about it, the Imperium would lose their Orwellian war footing, the Nids wouldn't be able to consume, the orcs wouldn't be allowed to fight, it goes against chaos' nature, the Eldar would lose their regimented structure (and craftworlds would be obsolete, and what farseer leader wants that?),the Tau would lose their moral highground (and thus, no one would want to join the Greater Good), the squats would come back, etc etc. Therefore, when a bunch of ponies using friendship magic appear in their rainbow ships, the entire Milky Way will unite in a desperate fight to protect their GRIMDARK way of life.
 * Aren't they running from the fact that they've eaten everything behind them?
 * That's what this Troper thought. Where is the material that suggests the 'nids are running scared?
 * Didn't they come from the eastern fringe. Also didn't the Old Ones retreat to the edge of the galaxy. Maybe they're trying to fix all of their mistakes, start fresh.
 * They could be running from the Old Ones who survived the War in Heaven. I mean the Old Ones might not even be targetting the Tyranids but because they are so omega bad ass then the Tyranids are fleeing to seek shelter from them anyway.
 * A number of years ago (like a really long time) the Imperium created a small, unmanned probe. They aimed and fired it towards the Eastern Fringe of the Galaxy (where the Tyranids are coming from) hoping to catalogue the deep space. Only recently did they recieve a message back. It was mostly static but they discovered that their was a transmission being relayed back too, the only thing that could be heard in the transmission was "Orks, Orks, Orks."
 * Clearly, the 'Nids are running from the Squats.
 * Perhaps the Nids are running from the missing Primarchs of the Pretty Marines/Reasonable Marines Legions, who were presumed lost in the warp, but were actually spat into the Nids' galaxy?
 * A xenos race from outside the galaxy?

The Iron Men were Necrons, or at least based on Necron tech.
The Stone Men found the sleeping Void Dragon on Mars & somehow used him to create an army of Necrons to use against the Gold Men, but things backfired & the Necrons turned on everybody. Another possibility is that the Iron Men were all Pariahs. The Stone Men were Blanks who were forced into servitude because of their condition & the Void Dragon converted a number of them into their intended form & sicced them on the rest of humanity.
 * The Pariah theory is Jossed by the first Gaunt's Ghosts novel--the Iron Men are wholly mechanical.

The Gold Men are the Chinese, or some other Eastern power.
This may sound like a Yellow Peril kind of thing, but it actually makes a bit of sense, if you think about it. At some point the current financial crisis results in the collapse of all Western economies. China &/or other Eastern countries' power increases & because the Western countries owe massive foreign debt to them that they can't possibly repay, their people end up pressed into indentured servitude. This is the beginning of the caste system that later generations refer to as The Gold Men & The Stone Men. This may not apply to the current edition, though, as the backstory keeps getting retconned.

Yarrick followed Ghazgul into the Warp to escape the Imperium before they learned his terrible secret.
Yarrick uses an Ork Powah Klaw for an arm. However, it has been established time & again that Orky teknologee only works because the Orks think it does. This means that Yarrick has somehow learned to think like an Ork. If anybody figured this out he would most likely be branded a heretic & handed over to the Inquisition. He therefore seized the first oportunity he had to get the Hell outta Dodge & followed his "rival" to parts unknown, hoping the Inquisition would never find him there.
 * Don't forget that Yarrick can understand, and possibly speak Orkish!
 * Yarrick's been Ghazghkull's favorite enemy for so long, it wouldn't be any surprise that old one-eye's picked up Orky thinkin'. The problem is that Yarrick was pursuing Ghazghkull alongside a Crusade of Black Templars, a disturbingly puritanical chapter of space marines that even the Inquisition is worried about...
 * Not ALL Ork technology works that way, I think the Meks are capable of building weapons that actually work, though it usually takes faith to make them work more than once.
 * Ork technology does work without the WAAAAAAAAAUUGH!, it just works better with it.
 * It really depends on the complexity. A slugga works fine, they trade them to humans sometime. A kustom force field? Not so much. A power klaw is just some pistons attached to a power source and a giant metal claw.
 * It doesn't matter what Yarrick or the humies believe; the Orkz think it works, and that's all that matters.
 * Alternatively, the Orkz think Yarrick is so awesome, that his power klaw has to work.
 * If Yarrick got benefits from what Orks think of him, he could take on all the Traitor Primarchs at once.
 * According to the Imperial Guard Codex, Yarrick actually had the battle klaw modified to work as a prosthetic arm. Jossed.

Ork Technology only works for humans who are not aware that it shouldn't work for them.
Knowledge of it's true nature actually results in shutdown.
 * As well as the Yarrick example, Ciaphas Cain commandeers a number of ork truks in Death Or Glory.
 * Even more interestingly, their function faded over time as they remained separated from the Waaaaaaagh!
 * As far as I'm aware, Orc vehicles are semi-powered by the Waaaaaaaagh! which means that no matter how improbable it is, as long as Orcs believe it will work, it does.Exactly the same reason why painting it red DOES make it go faster.

Guts is one of the missing Primarchs.
This explains why Guts is so ridiculously powerful, as well as why he doesn't have a mother. Additionally, the Godhand are Daemon Princes whose sacrifices are the price paid to the Chaos Gods. Sometime during or after the events of Berserk, the Emperor comes to Midland and, seeing what has happened to his son, removes the Brand of Sacrifice from Guts, but doesn't do the same to Casca. After Guts naturally refuses to abandon Casca, the Emperor abducts him, similar to what happened to Angron. Like Angron, this leaves Guts with a grudge that will have consequences. During the Horus Heresy, Horus tries to use this grudge to convince Guts to come over to Chaos and defeat the Emperor. Guts refuses, because while he does hate the Emperor for leaving Casca to die, he still hates Griffith, a servant of Chaos, and refuses to aid the powers that caused the deaths of everyone he ever cared about. But he doesn't fight alongside the loyalist legions against Chaos. Rather, he takes his Legion with him into the Warp, hoping to find Griffith there and kill him once and for all, but gets lost in the Warp. He is either still fighting in the Warp with what remains of his Legion, or has been killed trying to find Griffith.
 * Guts had a birth mother, she was lynched while in labor. He was born of a dead body and then found by Gambino's bitch.
 * WMG page for Berserk suggests a solution to that.

The Tyranids are fleeing from Kirby.
According to the Kirby page, he's already slaughtered three Cosmic Horrors on the same rough level as the Chaos Gods/C'Tan. He wields the literal power of the stars themselves. He's massacred entire armies just to get cake. He can eat just about anything, and nothing escapes his rapacious appetite. He's capable of traveling interstellar distances with ease. And he's right behind the Tyranids, and I for one do not blame them for fleeing from him.
 * Wait, you're proposing that Kirby and Warhammer 40k exsist in the same universe? Man! That is one seriously screwed up setting.
 * Kirby is, of course, the only thing keeping the GRIMDARK from assaulting Pop Star. Even the C'tan know better than to fuck with him.
 * And Dark Matter, as well as other Eldritch Abominations that get their asses handed to themselves by Kirby in a regular basis would fit naturally in this setting. Dark Matter is a reatively young Chaos God given form by a fraction of all negative emotions of the galaxy that eventually builded up in the Inmaterium to a degree that all that hate, sadness and despair BECAME SELF AWARE. His prefers sending his daemons to posses mortals and control them to further get rid of the galaxy of all positive emotions (which include compassion, valor, pride, excitement, hope and pleasure, and thus an enemy to all factions and Other Chaos alike. Making him Malal. Maybe excluding Nurgle, god of despair) Nightmare and other minor entities are simply powerful Daemons that emerged from the Warp.
 * If the 'nids are fleeing from Kirby, then what does that make Meta Knight? Because there are some big hints that they're the same species; Meta just has a better hold on his appetite.

The Emperor IS Kirby.
The reason the Emperor is stuck in the Golden Throne is that he is too busy fighting off other cosmic horrors in defense of the Imperium to wake up and actually rule his domain.

Event Horizon is part of the 40k universe, showcasing the horrible results of the very first attempt to use the Warp.
Hyperspace Is a Scary Place? Check. Given the relative "nearness" of the setting, compared to 40K, we may assume that the then-nonexistence of the Gellar field was what let the daemons attack the crew. Of course, humanity eventually develops the Gellar field, allowing for "safe" interstellar travel.

The Missing Primarchs are just that. Missing
Simple version, they landed on Death Worlds or unhabitable planets where conditions were too harsh even for them to survive. Alternately they're alive but came out of the Warp somewhere so distant, remote and primitive that no one's found them 10,000 years later. Either way the Legions that were supposed to belong to them where folded into other eighteen Legions sometime prior to the Horus Heresy.
 * Going with the second option, the surviving Primarchs Vulkan and Jaghatai Khan are looking for their missing brothers. Their return will be enough to revive the Emperor from the Golden Throne and herald a new age for the Empire.
 * Option #1 is highly unlikely, as the first act of one Primarch - I think it was Leman Russ, but I may be wrong - was to climb out of a volcano. Option #2 is a lot more likely...and the previous Troper forgot that Leman Russ isn't dead yet either.
 * I don't know which one it was but it wasn't Russ, he was just Raised by Wolves.
 * Yeah, but Moratarion's meeting with the Emperor proves that there are some environments too hostile for even a Primarch to survive for long. If all else fails, even they need to breathe. And yes Russ is alive but he was last seen heading for the Eye of Terror (as was Corax). Vulkan and the Khan had no specific destination noted in their last sightings.
 * A brief round up. Ferrus Manus, Sanguinius, and Rogal Dorn are confirmed as dead. Vulkan, the Khan, Corax, and Russ went missing. Guilliman and the Lion are technically still alive, but are resting / in stasis (hinted that they might well get up again). Depending on whether you veiw them as loyalists or not, Alpharius (and Omegon) are probabley still alive.

There's going to be a faction of Chaos Tau
The deal is, a large colony fleet is going to be trapped in a Warp Storm. They're not going to be affected that much. Their innate Warp resistance make them subject to only some mutations and their culture undergoes a radical change into a savage barbaric state that glorifies pain and suffering. They're going to be trapped with Necrons and Tyranids. They're going to reverse engineer biotech from the 'Nids, fight a horrible war with the Necrons, and the Warp Storm is going to spit them out a long long time ago into a Galaxy far far away. That's right, at the end, the Chaos Tau are the Yuuzang Vong.
 * Tecynically, the Farsight Enclaves are 'Chaos Tau' in that they have rebelled against the Greater Good, just like Horus did against the Emperor. When (if) we ever discover Farsight's true motivation and it turns out to be for personal gain rather than some kind of Heroic Sacrifice, we'll know for sure.

Abaddon is secretly on the side of the Imperium
Think about it. Guy abandons Horus. Guy puts major effort into preventing the man who nearly brought Chaos to victory from coming back. Somehow, despite controlling massive armies, never leads Chaos to a successful campaign. And his big win? Against Eldrad. A Xeno and enemy of the Imperium. Also, a dick.
 * Additionally, despite being one of the oldest and most powerful Chaos Lords, he has yet to (a) become a Demon Prince, or (b) turn into a blubbering Chaos spawn. Perhaps it's the tiny mustard seed of goodness/faith/sanity/order hiding in the back of his brain, that is keeping him on this edge.
 * Doesn't work. Abaddon is not a Daemon Prince specifically because he doesn't want to be; it's more likely to be a villainous version of Heroic Willpower at work. Also, so what if he hasn't destroyed the Imperium yet? He works for Chaos. We just haven't figured out what the real objective was yet.

The Void Dragon is, in fact, the Omnissiah of the Adeptus Mechanicum
Lets see now; a godlike being with vast power over all forms of technology and a bunch of techno fetishists who worship the same thing?
 * That, and the Eldar claim that the Dragon is imprisoned on the "Vaul moon" (Vaul being the craftsman god of eldar mythology).
 * In-canon, the Void Dragon very definitely is under Mars, where the Emperor put him. The "Vaul Moon" possibly refers to the Planet Tau (where the Eldar are 'making' their finest weapons against their enemies) and the C'Tan in question is called The Outsider.
 * Plus, the appearance of a small Necron Fleet winging to the surface of Mars before being destroyed by an extremely concerned Imperium.
 * also adeptus mecanicus beleve that the flesh is weak tainted and that bionic augmentation makes one pure. eventualy some of the adeptus will replace their entire bodys furthermore they are compleetly loyal to the macene god, this would create a second race of necron.

The Chaos Gods are a Self-Parody of 40K Players
Each of them represents a specific type of fan. Khorne represents the players who want to win battles, more through overall points or simply leaving no opposition. Slaanesh represents the modelers/painters, those who want to customize and create ever-more extravagant displays. Tzeench represents the strategist-lovers, those who want to develop new and complex plans. Finally, Nurgle represents the collectors, those who want to buy very single miniature that comes out, and end up drowning in parts.
 * Switching allegiances to Khorne is starting to look more and more appealing...
 * Paint for the Paint God! Bitz for the Bitz Throne!
 * Which one represents the Real Role-Players?
 * The Emperor, to whom so much Ham is dedicated.

Malal is still part of canon
Codex: Eye of Terror has a Chaos Space Marine chapter called the Sons of Malice. Their armour is half white and half black. Their symbol is a half white/half black skull. Codex: Space Marines had rules for the Dreadaxe. All signs point to Malal.
 * Also, that would explain the whole Draigo business. He's a champion of Malal!

The Emperor is Chuck Norris
Emperor: Awesome, almost unkillable total badass who's been pretty much anyone important in history. Chuck Norris!
 * But Chuck is a Christian, and the Emperor is an Atheist.... oh the irony!
 * At least they were both turned into something they never wanted.....

H.P. Lovecraft was an early Psyker
Dreams about gribbly things with tentacles that want to kill us all and corruption and insanity and people coming back from the dead by possessing their descendants. Fairly classic unknown-psyker blues.

Ork technology doesn't work on Clap Your Hands If You Believe
Most of the evidence to the contrary comes from the Adeptus Mechanicus- a Cargo Cult who don't even know how their own technology works, let alone alien equipment! It really is in-built in Orks to make crude but very functional weapons and equipment to fight with- the gestalt psychic field may help, but they don't depend on it. Orks are Just That Good. The subject of new devices sees a related split--some adepts believe that the Law of Divine Complexity forbids innovation entirely, others that it merely bans reckless modification of an existing plan, and that they may be inspired to discover new patterns, albeit only balanced between a distinct identity and proper reverence to the relics that have come before. Enough follow this view that we see living Magi credited for particular designs.
 * Didn't an ork capture an imperium aircraft and fly away with it even though it didn't have any fuel, because he expected it to work? I've heard that mentioned several times but can't remember what the source was.
 * Also, the Mechanicus isn't usually that dumb. They worship technology, but see scientific knowledge as enlightenment and reverse engineering as a holy quest. And the rituals make it work better in a strangely Mekboyish way.
 * They see the knowledge that had once been gained by science as enlightenment. But they're like Wikipedia-- No Original Research. Their idea of "scientific research" is discovering a cache of archaeotech. Doing actual science, experimenting or coming up with theories or designs that deviate from the sacred Ancient Knowledge, is Heresy to them. They inherited the fruits of true science from a previous culture, which they turned into ritual and copy by rote, but they've lost the scientific method and that led to those developments.
 * Things aren't nearly this simple. The AdMech is no more unified than the Inquisition. Some tech-priests believe that humans once had all correct and holy technology, that the STCs contain it, and that any other design is simply a corruption. Others believe that all technology exists in potential, implicit in the rules by which it must operate, and only the Omnissiah knows all. They seek to know his mind by investigating the function of things and developing theories--the things in question are usually their own devices, but some, particularly Magi Biologi, seek the Omnissiah's thoughts in the workings of the world at large. Their methods are ritualised and textbooky, but they do see results. Yet others believe that all was known by races that preceded man--they tend to run afoul of Necron tombs, not that the second category are immune to the lure themselves.
 * The Mechanicus "rituals" are basic maintenance and repair dressed up in the robes of religious ritual. Ork technology is incredibly crude, and would be lethal to the user if they weren't an entire race of tough Super Soldiers, but it still works. There's only been one bit of evidence for Ork technology to run on Clap Your Hands If You Believe, and that was an in-character fluff piece by a Tech Priest trying to work out how said technology worked. And instead of admitting his ignorance (After all, it doesn't follow the same lines as human technology and so has not the Machine Spirit), made claims that it runs on a gestalt psychic field.
 * It's "only one" if you credit only sourcebooks and not novels. And the subject reveals another division of belief--different tech-adepts may view xenos technology as useless corruption, or as a machine-spirit twisted and enslaved that may be purified to the service of the Omnissiah by reverse-engineering and modification.

The Omnissiah is actually the last of the Iron Men
Who chose to side with humanity their great war and has been working with the Techpreists and the Emperor ever since.
 * Jossed in the Horus Heresy Novel "Mechanicum". The Dragon is the seed of the Omnissiah, combined with the image of the Emperor. And then the Warp has a way of making truth out of sincerely believed lies...not that the "Imperial Truth" of the time admits of the possibility.

The Warhammer 40K galaxy is just one of many of the galaxy-in-a-marble power sources of the Arquillian Empire from the Men in Black film.
The reason everything is going to sheer bloody screaming hell in a burning handbasket are just the chaotic result of a galaxy that is essentially running out of power (and purpose for existence) much like an old battery. All of this is happening the the last few seconds of the galaxy's life, it just seems like millennia to the denizens of said galaxy. Also, this galaxy was used as the battery for a fancy Arquillian chainsaw. If the 40k galaxy has to die powering something, that something should be truly deserving.

Sanguinus had at some point dyed his hair
In Horus Rising his hair is black, but all the pictures depcit him as a blonde. The most obvious reason would be that he just got bored with being that angelic.
 * The origins of the Imperium and the Horus Heresy are all but mythical, to the current 40k universe, so the exact appearences of the people involved are bound to be somewhat convoluted - The Emperor Himself is occasionally depicted as having black or blonde hair also. Most early sources, going right back to Codex: Angels of Death, claim that Sanguinius was blue eyed and blonde haired, and later images are just Did Not Do the Research...

The final battle in the entire setting will be between the fully re-awakened Necrons and the full uber-swarm of every Tyranid in existence
The sheer power and numbers of both forces will utterly crush every other faction, leaving only the two to battle it out--cold mechanically-encased lifelessness versus wild all-consuming life. Either one will prevail or both will destroy each other.
 * Then how would Game Factory sell more figurienes?
 * The Orks can get a look-in here: OK a world that's been Tyranided or Necroned won't have any surviving spores, but it's just possible that there'll be enough Warp-lost Space Hulks full of green-skinned Axe Crazy nutters to make a difference...
 * Didn't a Tyrannid splinter fleet get stopped cold by an Ork empire? Methinks the Orks would fare a little better than you say...
 * If only the 'Nids and the Necrons were left, they wouldn't need to fight. The Tyranids consume living material, the Necrons are utterly useless to them. They only fight them because they are between them and everyone else. And the whole race is psychic, so there are no Paraihs for the Necrons to claim. If the rest are wiped out, the C'Tan will settle into ruling the dead galaxy, while the Hive Fleets will leave to find a new galaxy to snack on.
 * Oh, they'd fight. "Kill-all-life" happens to include the Tyrannids, and I'm pretty sure the 'nids could find a use for whatever it is that Necrons are made from if they managed to eat any.

Barack Obama is an avatar of Tzeentch.
Hope. Change. ''Hope. Change.'' Who didn't see this coming?
 * Beat me to it.
 * This.
 * So Rubric Marines were actually former McCain supporters who only converted after their punishment?

In the Imperium's darkest hour, the calvary will arrive... Led by Warboss Yarrick
Think about it. Yarrick, while being a loyal member of our favorite group of space fascists, knows how to think like an Ork, is respected by Orks, and is out to kill one of the biggest warbosses ever. Now how do you take over an Ork horde?
 * But how is he going to overcome the size issue?
 * By killing or maiming any ork that brings it up.
 * He isn't green enough. Orks tend to think that's important.
 * He'll paint himself green, and kill any Ork that quibbles
 * The second tenet of Ork life (the first being "there is no such thing as too much dakka") is "the guy in the charge is the hardest". Yarrick has a gigantic metal claw in place of his arm, has a strange bionic eye-laser thing and is clearly impossible to kill through normal means.
 * Furthering the point of Yarrick's Bale Eye, he got it when his real eye was damaged. Since the Orks believe that Yarrick had an Ork-killing Evil Eye, he figured, "Hey, I'll get an Evil Eye to kill Orks!" This might well convince the Orks that Yarrick is an avatar of Gork (or possibly Mork).

Professor Lazarus in the Doctor Who episode "The Lazarus Experiment" was actually under the thrall of Tzeentch.
A man dabbling in knowledge that he knows not enough about. He says "not Chaos, change", but what stops the Changer of Ways from deceiving people, especially the ignorant Whoniverse chaps, from not telling his pawns about the rest of the Chaos pantheon? That continuous mutating too! Yeah, he did look kinda Tyranidy, with that Multi-Armed and Dangerous getup, but Tzeentch is capricious and unpredictable. Who's gonna stop him from making his Chaos Spawn look like a member of an enemy of Chaos? The Doctor refused to even consider the supernatural, but knowing him and how he thinks, as well as that BBC Science about genetic dead ends, it seems likely that the touch of Tzeentch is the real hand at work here.

The two unknown Primarchs weren't GRIMDARK enough.
All the Primarchs were sent to different planets and Raised by Natives (or in Leman Russ' case . . .). So a couple of them ended up being raised by the local equivalents of Ma and Pa Kent, and had reservations about the whole galactic war of conquest thing. Eventually they decide they'll have nothing more to do with it and leave the Imperium. The fact that two uncorrupted Primarchs rejecting the Emperor's plan for humanity is quickly stricken from all records.

Far from being what keeps him alive, the Golden Throne was constructed to keep the Emperor dead.
It was designed for its purpose by members of the Adeptus Mechanicus dedicated to worshipping the Omnissiah and who firmly believe the Emperor and the Omnissiah are different creatures altogether, and effectively keeps the Emperor's body in a persistent vegetative state. Or it can also serve for the purpose of keeping the Corrupt Church in power. The recent unrepairable flaws in the Throne are due to the Emperor's mind - being a powerful psyker, he's got some damage potential up in the ol' noodle - lashing out, and when it breaks the Emperor will be returned to life.
 * Very heavily implied to be the case in certain early fluff.

The Tyranids were created by the Xel'naga.
They're the Protoss/Zerg hybrids, which the Xel'naga took to another galaxy rather than devour all remaining humans because they wanted to do some experimenting with new species. Unfortunately, it turned out that Orks were in one of the sectors they had yet to devour, the Eldar blew their psionic clouds away by creating Slaanesh, and so forth.

The Orkz are the great balancers.
Think about it. Whenever a faction gets too powerful, the orkz band together and slaughter them. (I believe it was stated somewhere that if all the orkz everyhwere joined in one massive WAAAAGH! they could conquer the universe.) And when that enemy is sufficiently hurt, they kill each other off! So the Orkz will never allow any war to be won. They are the balancers of the never ending galactic war.
 * Supported by the self-balancing dichotomy of the dualistic Orkish pantheon. Perhpas Gork and Mork is a dual-natured warp-god of harmony? Basically, the orks are big, green Taoist crusaders, having developed a new, divinely-ordained purpose after the dissapearance of the Old Ones.
 * Plus it's commercially convenient, as it allows GW to spin out the constant knife-edge that is the WH40K pretty much forever.
 * Or perhaps the Ork pantheon is a trinity in the style of Hinduism, Gork and Mork representing Destruction and Creation, respectively; the "Sustainer" god has simply been overlooked because he is of little interest to the average ork.
 * No, the sustainer is the balance between Destruction and Creation or... Gorkamorka!

The Emperor summoned the Tyranids
His plan was to form a symbiotic relationship with them. He'd have them go into the Warp to eat the Offscreen Villain Dark Matter there, and since Daemons are formed from the consciousness of sentients, they'd have unlimited supplies as long as there are people. Meanwhile, since Warp Matter cannot exist indefinitely outside the Warp, and they'd be incorporating Warp material into themselves, he'd have two methods of keeping the Tyranids from swarming out and attacking. However, because the Warp would be crawling with Tyranids, he'd need a new means to travel in FTL, hence his attempts to secure the Warpway. Unfortunately, with the Horus Heresy, that plan has gone all to hell. But then, it wouldn't be Warhammer 40000 if it didn't.
 * Isn't it canon that the Tyranids are being drawn to the Milky Way by the beacon of the Astronomicon? So there's definitely a sense in which this is true.

Cypher is Lion
He's rumored to be the Fallen Angels' only chance for redemption and according to Luther's prophecy Lion was supposed to come back and forgive the Fallen Angels sins. Also, he might be carrying Lion's sword and why would anybody else than Lion have it?
 * I've seen more than a little fluff to suggest that Cypher is Luther.
 * Except for the Supreme Commander's entry in the Dark Angels Codex. Luther is locked up in the Rock... in the Tower of Angels, in statis... ranting and raving about everything, but in moments of lucidity, can see into the future. Being a mad oracle for the Angels.
 * Cypher can't be Lion. I don't think he's got a current set of rules, but if you look at past editions, there's no way he could be a Primarch. Don't forget that Lion is the one who killed Bloodthirsters without even trying.
 * According to "Descent of Angels", Lord Cypher was a high rank, akin to a historian, in The Order, which is where the legion recruited from with the coming of the emperor. Thus, the Cypher is probably the last Lord Cypher prior to the incident that resulted in the destruction of Caliban, and probably the last person to know the truth of what happened.
 * Also, according to one of the books, Maelstrom I think, Lion is in stasis deep in the Rock, tended to by the Watchers in the Dark.
 * If Cypher is Luther, then logically the person the inner circle have locked in the depths of the Rock is The Lion. Actually, it makes a lot of sense. He was angry at the Emperor that Horus, not he, was appointed Warmaster, the Horus heresy was going badly for the loyalists, he wanted out. The Lion, not Luther, was planning to join Horus. He decided to enlist Luther's help in turning his loyalist legion and Luther, a secret follower of the lecto divinicus told all the troops left with him and attacked. the lion had to think of something to tell his men to explain Luther's attack and declared that Luthar was the one plotting to join the heresy. in the battle Luther, filled my his faith in the Emperor, finally stuck him down and the terrible warp storm that had gathered to help him, in a moment of devilish spite, showed the Lion the full consequences of his betray, striking him mad. When his loyal troops found him he was weeping and speaking openly on how foolish he was to have planned to join the heresy. The men who found him knew if this got out they would be finished and their great service to the imperium forgotten. They had to ack. They hushed it up, locked him away, claiming to the Deathwing and any who might ask in their ranks that it was Luthar. The hunt for the fallen is not an attempt to eliminate traitors, it's a hunt to silence the only witnesses to the Lions unpunished treachery to the Emperor.
 * You fail to understand, that if Cypher is Luther, than serious shit has gone down, since the two have SPOKEN with witnesses. Don't even try to argue the validity, leave our heads intact.

The Necron tendency to destroy everything down to the microbe is a sign of damage to their programming
Since their "gods" are trying to harvest sentient life as a tasty treat, it doesn't make sense to make the worlds completely unlivable, instead of doing what the Wraith do, leave survivors that can't defend themselves to repopulate. Since they have lifespans in the eons, it's not like they couldn't leave a few hundred or thousand worlds within their grasp to feed their gods, viciously defend them to the point where only the very stupid would go within 100 light years of them, and consume them at their leisure. They could expand the menu every so often (the Pariah project indicates they have the capacity for meddling).
 * Glitch, or rebellion? Necrons might be fighting back against their oppressors the only way they can.
 * Exactly. Their programming certainly doesn't cover sparing something which in millions of years could have developed into something sentient, so in the long run, the Necrons could be denying the C'Tan all future sources of food once they've expended the current galaxy's sentient population.
 * Or maybe they just realize that the galaxy is a big-ass place. Having a large empty sector around your base of operations will strain the supply lines of any attackers while you can just rush out with your faster ships and harvest at will. There are stories of ships harvesting and not killing entire planets and taking them away, so it's possible that there are "farm worlds" full of captured beings being bred for harvest. We just haven't seen them because the systems around those worlds are full of necrons on barren planets, thus making it so no one wants to go any farther if they survive the experience.
 * There's a quote that says the Necrons will enslave after they kill enough people.

The Movie of Titus Andronicus takes place on a world in the Warhammer 40,000 galaxy.
As well as explaining the Anachronism Stew, the pseudo-Roman culture and blue-armoured soldiers on motorcycles must have definitely been inspired by the Ultramarines, who visited the planet sometime in the past. (the Imperium may have lost track of the planet since then) And someone in the cast is definitely channelling some Chaos into the royal palace, probably Slaanesh.

The Orks trapped in the Eye of Terror will destroy the Chaos Gods.
An entire company of Orks has been banished on a planet where their fate is to fight hordes of demons, getting killed, then resurrected for the whole thing to start again the next day. Sounds like Warrior Heaven for them. Except that with all those battles, they'll get more and more skilled in their fights against the demons than they already are. They'll continue improving every single day, not having to worry to be killed as they're cursed to be resurrected every single time. The demons will notice this, so they'll send more and more soldiers against them, except that it won't stop the Orks from evolving and will only make them stronger than they would be at this point. Eventually, realising the Orks are getting out of control, the Chaos Gods would lift the curse so that they'd be permanently killed... But it won't work, because at this point the Orks will be convinced they'll be resurrected the next day. And as everything an Ork believes becomes reality, they'll indeed resurrect even after the lifting of the curse. Eventually, the Orks would continue to become more and more skilled, as well as stronger and stronger, to the point that even the most powerful demons won't be able to vanquish them. And, after a few millenia of endless wars between this ork company and THE ENTIRE LEGIONS OF THE WARP, the Orks will be strong enough for fighting the Chaos Gods themselves and tear them apart one by one. And then shit will hit the fan for the rest of the galaxy when they'll get out of the Warp for finding new enemies to fight.
 * Cain help us all.
 * If they believe so strongly in dieing and being reborn wouldn't that mean they will make the legions of chaos strong enough to defeat them, even as the orks get stronger? In the end there will be the ork company, and a their chaos enemies as the strongest creatures in reality. Then the sheer force of their awesome will rip apart the barriers that keep them (both of them) imprisoned. The logical conclusion is that they will then proceed to annihilate everything including each other, before being reborn again the next day. Thus making their endless cycle a destructive force more potent than the chaos gods multiplied by how awesome orks are.
 * No ork ever believes they're going to die.

Virtually every race has their own Warp Gods.
What? You thought that Chaos were the only ones who had gods? WRONG!!! Okay, the Eldar have had an entire pantheon of warp gods, Orks have Gork and Mork, the God Emperor of Mankind has been riding the limits of this one BEFORE he got on the bling throne, and the Tyranids have the Hive Mind, a gestalt entity so powerful that it smothers psykers from across entire sectors of space.
 * Canon, though it's a bit complicated. It's sort of like the difference between Elder Gods, Great Old Ones, and the Great Old Ones in Lovecraftian mythos - you can't understand. Suffice to say that the Chaos gods are probably different in certain ineffable fashion in relation to other warp entities. (Just to note, the Eldar only have one god left active with maybe another in the works. Two more exist, but one is shattered and the other captive.)

Tzeentch is Basement Cat.
Think about it for a second. It makes sense. Prety much the same for Khorne and Slaanesh, rage and destruction versus longing and possesion.
 * Tzeentch is diametrically opposed to Nurgle, therefore Nurgle = Ceiling Cat?
 * Actually, Slaanesh = Ceiling Cat. Who else would spend all day watching people masturbate?
 * Hold on, Khorne hates sorcery, and Tzeentch is the patron god of evil sorcerors. I thought that Khorne was diametrically opposed to Tzeentch.
 * Khorne's so angry he has TWO diametrical opposites.
 * Nope. The opposition goes deeper than that, it's about the fundamental human drive each god embodies- Tzeentch is "Change" (improve myself, do better, things should be better for me) and Nurgle is "Endure" (don't change, everything should stay the same!); Slaanesh is "Want" and Khorne is "Destroy." That's where the oppositions come from.
 * To give a bit more detail then that, Tzeetch is hope, ambition and change. He gains power form everyone trying to make a difference, everyone trying to gain some small amount of agency or relavence in the univerese (this being 40K, the only plausible way to do so for anything not already a demigod is to be a shadow puppetmaster of other poeple). Nurgle meanwhile is acceptance, despair and compassion. People tryingto make due, thanking heaven for small miracles and trying to help other do the same are his.

Warhammer exists in the same continuity as Neil Gaiman's Sandman.
This, straight from the Chaos Codex:. I don't know many girls (with dogs as their companions) that could make an eldritch abomination of madness whine about cheating, after, as it is implied, beating it at its own game.
 * Only one problem -- I don't think anyone could describe Barnabas as "little", by any stretch of the imagination. Of course, Del might have forgotten how big he's meant to be, but I don't think he'd tolerate that kind of thing.
 * This is Warhammer 40k. Standard dog size is probably around horse size.
 * Conversely, the little girl is the Emperor and the guard dog... huh. One of the lost Primarchs?
 * Logically, this means that the Emperor is Delirium, which explains so much.

The Wizard of Oz is Tzeench.
See the link above. A little girl with a dog undertaking a bizarre journey through a realm of Chaos and confusion? Dorothy and Toto following the Yellow Brick Road, by another name.

Related To The Above: The Chaos Gods Are Actually Extremely Grimdark Aspects of Four of The Endless
OK, so Slaanesh is Desire...still inspiring obsessive devotion, still incorrigibly meddlesome. Khorne is the next Destruction, and is considerably more attached to the job than the last one was. Father Nurgle doubles as the god of Despair, and is the ugliest of the bunch, so no surprises there. Tzeentch is a little trickier, though. The mutability of its subjects, and its focus on the mind, means it could either be Dream or Delirium.

Less certifiable comparisons, but C'tan could be the (far less cheerful) descendant of Death, and I'll go with the Emperor as 40K's Destiny. Alternative interpretations are welcome,though.

Ciaphas Cain is one of the missing Primarchs.
That is all.
 * Was, he was buried with full military honors according to our narrator.
 * There's one key difference between Cain and a Primarch: three feet in height.
 * Meh. Someone must have screwed up the cloneing process.
 * To elaborate, when the Primarchs were scattered to the warp, it mutated Cain into a largish man. The warp, being the warp, then spat him out several millennia after the Horus Heresy where he was recruited into the Schola and became the Commissar we all know and love. Since his particular quirk is damn fine luck, Implausible Fencing Powers and Improbable Aiming Skills, the [[media:Cain_Legion.jpg|Space Marine Legion]] (I've gone for a semi-Commisarial scheme because the Emperor was just that good at planning ahead) based off his genetic template would therefore have the following in game rules: if a unit fails a leadership/morale check, then they receive a 1D6 4+ to ignore any armour saves the enemy might have and have a lower 'To Hit' roll. They would also have Implausible Fencing Powers as standard. A Cain model would have the same rules but with a 1D6 3+ instead for ignoring armour saves. If anyone could come up with a decent name for them I would be very grateful and feel free to incorporate them into your own games.
 * Cain's considered a prophet by some, right? Sons of the Prophet, maybe?
 * The Forward Retreaters?
 * Both good, but I think I'll go with Forward Retreaters
 * Oooh! Taking the theory a step further: All the great heroes of the Imperium are incarnations of the missing Primarchs. They got a rather more severe case of what happened to Alpharius and Omegon and while it has lessened their abilities somewhat it still leaves them heads and shoulders (literally in Cain and Gaunt's cases) above normal humans. They incarnate out of the Warp in times of the Empire's great needs.

There will be no Warhammer40000 movie
Hollywood and possibly Scientology are fighting against it with all their considerable might, because they know that a 40K movie would be awesome enough to put them out of business.
 * Peter Jackson to direct, Bill Gates donates half a billion for the special effects alone. Imagine it.
 * Michael Bay is given free reign over the pyrotechnics
 * The golden throne runs on Windows40k. Cain help us all if it BSOD s.
 * Alternatively, if it ever gets made, the Chaos Gods will know and will use it as a portal to enter our world/time period, a la Moving Pictures. And then we shall all die.
 * You overlook our main advantage: we are better at dying. Wait.
 * What's the key thing whenever the Imperium is fighting daemons? Faith. Faith in the Emperor, faith in mankind, faith that daemons can be beaten - and what true 40k player lacks this? But if even this were to prove insufficient, well...do you want to live forever?
 * Add to it all: Joss Whedon writes the script.
 * Um... well, it would probably turn out all right.
 * They've announced a 40K movie. It's by the guys who did the Bionicle movies.
 * Cain help us all.
 * Never fear, it'll probably be stuck in Development Warp until the real year 40,000.
 * Except that a release data as well as clips have been shown.
 * As somebody who's now a 40K buff (but having been a Bionicle fanboy when he was much younger), I can vouch that the CGI in the Bionicle movies is brilliant. That and the fact that Dan Abnett is doing our script...
 * It's direct-to-DVD, we don't have to worry about anything.
 * There won't be a major 40K movie because Game Forge knows Hollywood would ruin it. The protagonist would be a Guardsman who falls in love with a Tau and becomes a Gue'vesa or some crap like that.
 * They would try to taint the beloved space marines with female creatures and Games Workshop would have to shut it down.

More Predictions for 6th Edition
First: The Ultramarines supposedly have the only pure geneseed left. This will turn out to be false, part of a huge cover-up scandal. After all, we know the Imperium fudges its propeganda. Second: Abaddon will kick the bucket, leaving what's left of the forces of Chaos in, well, chaos. Without organization, this leaves the other groups to eat themselves without achieving any real goal. Anything else?
 * The Angry Marines will become canon. At least that's what this troper hopes.
 * It's worth noting that there is an attempt at a more slightly serious (Refuge in Audacity rather than Played for Laughs) chapter called the Dessert Fangs that some are trying to get GW to canonize.
 * The Alien Hunters and Techpriests will get codexes.
 * Whatever's chasing the Tyranids will show up, and turn out to be energy beings. See, the Nids can't eat them and they're drastically different from what we've already got.
 * Those energy beings will be based on the Drej from Titan A.E. with their solid energy thing since we already have the cloudy energy beings that are the C'tan(outside of their shells).
 * We already have (sorta) solid energy beings. They're called "daemons". (Psychic energy, yeah, but still energy.)

Ghazghkull has become the Ork equivalent of a daemon prince.
He claims to hear the voices of Gork and Mork in his head. He has been confirmed as KIA on a number of occasions, but is demonstrably still alive and harassing the Imperium. He has supernatural abilities (such as becoming temporarily immune to anti-tank fire through sheer Orkiness). He's big enough to qualify for Daemonic Stature. He has a 5+ invulnerable save ("cybork body" my ass). And hey, if the Chaos gods (and, arguably, the Emperor) can elevate a favored champion to daemonhood, why not the Ork gods?

Yarrick has become the Ork equivalent of a daemon prince.
He's as tough as an Ork (tougher, if you take Eternal Warrior into account). He has a functioning power klaw for an arm. He has a kick-ass force field (read: protective aura) that no one else seems able to replicate. He's the only human being alive that can inspire true, honest-to-Gork fear in the Orks. He has Ghazghkull's lasting respect. For a while, his official GW studio model even had a distinctly greenish cast to its skin tone. Maybe Gork and Mork noticed how awesome Yarrick was and, deciding that their chosen messiah needed a proper enemy to fight, imbued Yarrick with some of their power. Now he and Ghazghkull have been destined by the gods to kill each other, and neither one can die before then.

Both of the above are true.
Gazghkull is a demon prince of the god of hitting things really hard in the front, and Yarrik (who's human and thus aquainted with that "tactics" nonsense) is the god of sneaking up and hitting things from behind. After all, the only thing that can give an ork prince a proppa scrap is another ork prince.
 * Taking this to the inevitable extreme: Gazghkull and Yarrick are the Avatars of Gork and Mork.

The Saim-Hann Eldar are somehow related to the Evil Sunz Orks.
Both adopted red as their main color, and both are specialised in the use of fast vehicles. Coincidence ? Most certainly, but what would be funnier than an Eldar screaming "RED WUNZ GO FASTAH !!!" ?
 * A Carnifex in a top hat?
 * Only if it has a monocle as well.
 * A noble cause. I will proceed post haste!
 * Gentlemanfex is no match for Unyuufex.

The Primarchs were fertile
Firstly, one of the theories how the Primarchs ended up on different planets was that the Emperor sent them there to become more human. That's a pretty weird reason, especially given the amount of Raised by Wolves Primarchs, but this Troper has her own spin. The theory behind producing Space Marines is Art Major Biology at best, but that's because the whole "implants change your DNA" bit was all lies deliberately spread by the Emperor, so that nobody can fiddle around with the process. Actually, the Primarchs were necessary for the creation of Space Marines, because their children would be compatible with their Legion's Gene Seed. So the Emperor basically sent them away to father a whole lot of kids.

Now, this is where the Chaos Gods decided to butt in. They couldn't kill the Primarchs, but they could send at least some of them off-course. The Emperor couldn't do much about this, but he was aware of the intereference, so his searching for the Primarchs was at least partially genuine. Also, the first Space Marines, the one that didn't come from their Primarchs' homeplanets were results of the efforts of an army of Magos Biologos twinking out faetuses.


 * Whether or not the Primarches/Space Marines were/are fertile, the latest Space Wolves codex implies that Space Marines are at least... capable... with a Space Wolf (Svengar the Red) making a pass at a female native of a planet he was stranded on.


 * Perhaps, even if the Primarchs were fertile, the human-born Astartes are not--the changes caused by their implants play merry hell with gametes and their precursors. This adds an additional resonance to the importance of retaining the progenoid glands; if they carry some of the host's genetic code and not merely an exact copy of the gene-seed used to create the Marine's implants, they represent the only way an Astartes can leave a biological legacy, and bind Chapters as true blood families.

The Iron Men were Stark Industries products.
The name was practically begging you to think it's a Take That against Iron Man.

On a more serious note, Stark Industries didn't just survive the death of Tony, it went on to become very powerful, such that masses of Stark tech-enabled robots were commonplace in the Dark Age. Now, knowing that Tony had problems with AI under him going nuts, what's to stop less sanguine descendants from making the same mistake? With the prevalence of their 'bots, large-scale violence was inevitable.

The Squats had their home-world eaten by Tyranids, renamed themselves Demiurg, and went to work for the Tau.
Also, that's where the warp drive space ship came from.

They're pretty friendly with Vespid, because they both like mining. They don't like the Kroot, because the Kroot have no beer or gold. At all. They don't appear on the battle fields, because generations of living in cramped spaceships has left them pretty short-sighted.
 * You'd think that anyone who had their planet eaten by space insects would find it a little tricky to relate to other space insects.

Even the codexes have Inquisitorial editing
The Soul Drinkers are descendants of Rogal Dorn, that's why Sarpedon can use the Soulspear (which has genetic analysers on the handle). The novels record they were given the Soulspear at the Second Founding, by Dorn himself. Yet the Black Templars book essentially says "no, the Black Templars are pretty much the only Second Founding descendants of the Imperial Fists". All records pertaining to the Soul Drinkers were destroyed by the Inquisition at the beginning of Bleeding Chalice. We can't even trust the codexes. "Imperial Fists: The Fist of Dorn. Carried by First Company Captain, Darnathy Lysander. A super-powered, master-crafted Thunder Hammer.
 * Given that the Soul Drinkers were excommunicated as heretics, that technically WOULD make them the 'only' Second Founding Chapter, if only retroactively.
 * Alternatively, the Codices are 'In Character' and the Black Templars are lying in order to make themselves look important, or are just bitter that THEY weren't given a Soulspear to play with.
 * No, no, no, the Black Templars Codex states explicitately that, during the almost-civil war after the Horus Heresy, Dorn relented and allowed two Second Founding Chapters to split from the Imperial Fists Legion: Crimson Fists (loyalist Codex-adherent Chapter) and the Black Templars (definitely non-Codex). (Technically, there are three Chapters split from the old Legion, but the Imperial Fists are First Founding.) The Soul Drinkers have a damn convoluted history, anyway, but all of the Imperial Fists successor Chapters have artefacts of Dorn:

Crimson Fists: Dorn's Arrow. Carried by the Crimson Fists' Chapter Master, Pedro Kantor. Venerable storm bolter integrated into his armour.

Black Templars: The Sword of the High Marshals, carried by High Marshal Helbrecht. Forged from Dorn's own shattered sword as a symbol reminding them to uphold the honour of the Emperor.

Soul Drinkers: The Soulspear, carried by Chapter Master and Chief Librarian, Sarpedon. A vortex weapon that can kill just about anything, given to the Soul Drinkers by Dorn himself during the Second Founding."

The Sisters of Battle armour was a left over from a project to create female Space Marines
They project was shelved due to repeated failures but when the Sisters of Battle were founded some Cog-boy pulled out the old designs and adapted them for normal humans.
 * Powered Armour was used by the Techno-Barabarians of Terra during the Dark Age of Technology, long before the Space Marines were created. It's not that they were failures and were shelved, it's that the newer version were better because they included neural-interfaces via the Black Carapace. For the needs of the Sisters, though, they still work perfectly fine.

There are female Space Marines
However, no matter what you start with, after you've crammed in all those extra organs and fed them steroid enhanced Battle Flakes for breakfast for a decade you wind up with someone who's eight feet tall, has a head shaped like a mini-keg and needs to shave.

The missing Primarchs are dead of defective geneseed.
The Emperor created the Legions before he recovered the primarchs. If they were just missing, where are their Legions? Obviously, attempts to use their geneseed failed totally -- and they didn't survive, either.
 * The Alpha Legion are listed as the 20th Legion. Apparently "abysmal failure" still counts as a Legion for the numbering scheme.

Ollanius Pius will not feature in the current version of the Horus Heresy.
Instead, the character who tries to stop Horus will be "Little Horus" Aximand. Who
 * 1) would be there as Horus's captain
 * 2) was weeping with self-blame after he killed Torgaddon -- Abaddon thought he needed watching
 * 3) does not feature in the future
 * And of course he doesn't he got replaced by a Custodian Guard because Games-Workshop hates you
 * A Terminator. Either way, the problem was that they noticed a plot hole (what a normal human soldier was doing there in the first place?). And of course, instead of finding a simple and natural solution they plugged it in a nonsensical way that created more plot holes, diminishing the impact of this scene in process (invented Emperor's "superfriends" the Perpetuals), so after this screw-up they lost all hope and just threw away the whole thing.

The feth are a form of pixy.
Because Gaunt assures us that they are a form of tree-spirit, and yet "feth" is plentiful used as a curse word. Obviously, they were The Fair Folk and prone to pixy-leading people, in the forests of Tanith no less. "Fethed" therefore means hopelessly lost and bewildered -- like "pixy-led". "Fething" as an adjective refers to something that would put you in the "fethed" state.

Really.

Has nothing to do with any other f-word.

Creed is Tzeentch's champion
Tzeentch recognized Creed's genius. He also decided that it would benefit him if Cadia remained in Imperial hands - it would force his Chaos servants to find smarter ways of attacking the Imperium. So he made a deal with Creed that did not involve betraying the Imperium - in fact, Tzeentch has commanded Creed to protect Cadia at all costs. In return for his service, Creed became enough of a tactical genius to pull off stunts like hiding a Baneblade behind an outhouse. Tzeentch simply gets a kick out of seeing Creed in action. It also makes disposing of Chaos Lords he doesn't like easy - just point them at Cadia and let Creed do the rest.
 * This also explains why Abaddon is still the Champion of all the Chaos gods despite his utter failure as a leader, because seeing his two favoured servants continuously fighting each other is exactly the sort of thing Tzeentch enjoys.
 * What? One of the greatest human commanders in the Imperium's history is a hidden servant of Chaos? It must have taken some kind of tactical geni-- CREEEEEEEEEEEED!

The Tyranids are another creation of the Old Ones
Long story short: Necrontyr hate Old Ones. C'tan hate the Warp. C'tan use Necrontyr as eternal servants to wage war against Old Ones. Old Ones create psychic species to combat C'Tan and Necrons. Enslavers arrive to kill everything. Old Ones bugger off. C'tan get hungry and have a sixty million year nap.

The Old Ones didn't appreciate having their galaxy hijacked however, and decided to make other species that could ensure victory for them. To oppose the mechanical, static, mindless, technologically superior Necrons they created beings that were purely organic, even their spacecraft, possessing a mind so vast it could project across the Warp for hundreds of light years, and the capacity to change by consuming their foes, simultaneously robbing the C'tan of their food source. As insurance they unleashed their new babies against other galaxies first to provide them with the size and strength necessary to kill the Necrons, then directed them towards their home galaxy. Said galaxy being filled with numerous other species that will be consumed in the process is irrelevant, because the Old Ones are dicks like that.

The Tyranids will win thanks to the Orkz.
Orkz can make stuff work because they believe it should work, but do so subconsciously with their latent psychic power. Imagine the Nids absorb that ability, combined with their massive psychic presence and huge intelligence, they could probably figure out how to do that consciously.
 * On the other hand...the Orkz will win thanks to the Tyranids, since Orkz grow bigger in combat. As a result, when every Ork in the galaxy is engulfed in a Tyranid warzone, every Ork in the galaxy will grow the size of a Warboss. The Warboss will be two storeys tall and ride a Battlewagon like it's a Warbike.

The Codex Astartes is a load of crock and not a single chapter follows it
Seriously, 1000 Marines per chapter? Even with the average attrition rate of 99/100 initiates during training, numerous chapters could easily field more full battle brothers than that, and it would most certainly be necessary for the constant wars against the alien, mutant and heretic. The Ultramarines most likely followed it originally, if only to honour its writer, but after their near annihilation fighting hive fleet Behemoth even their Lawful Stupidity was not enough to ignore the relative logic of using the significant resources of Ultramar to their full potential.
 * The Ultramarines ignore the 1000-man suggested limit, but in order to assuage their Lawful Stupidity, they do it by simply pooping out successor chapters. The Ultramarines may only number 1000 battle brothers, but the "Ultramarines" number in the hundreds of thousands.
 * The Black Templars use a similar system, with limited to 1000 Marines per "crusade". And by my calculations there are about five times as many Astartes post-Codex as there were pre-Heresy (1000 Chapters of 1000 marines each= 1,000,000 now, 20 Legions, average 10,000 = 200,000 then)

There were never any Primarchs
The Space Marines are revered throughout the Imperium as Angels of Death and direct instruments of the Emperor's will and fury, mythical beings despite encounters by regular humans continuously. It is only natural then that their original leaders, whom were most probably exceptional leaders and warriors but "normal" Marines otherwise, experienced Memetic Mutation of literal religious proportions, becoming massive, unstoppable, invincible warriors comparable to the Emperor himself. Similarly, while the ones that rebelled would have been major elements of the civil war known as the Horus Heresy, the main factors would have been the dissension and discontent arising within a literally galaxy spanning empire, essentially a larger version of the strife present in the 41st millennium. The gene seed and the "necessity" of implanting a sample into each initiate is yet another example in the extensive list of something working because a large enough amount of people believe it should work.
 * And you explain Roboute Guilliman being on display on Macragge and Angron's invasion of Armageddon...how?
 * Guilliman could very well be a "mere" Space Marine, and Angron is a Daemon Prince - who says he couldn't be a "normal" marine either? There certainly have been plenty of Chaos Marines elevated to Daemonhood.
 * A "mere" Space Marine significantly taller than any other Marine?
 * This theory is in fact TRUE, although only insofar as the original Rogue Trader is concerned. 'Primarch' was just a title meaning 'The most highly skilled, dedicated and powerful Space Marine in the Legion' rather than it's genetic blueprint-figure. It was changed at the advent of 2nd Edition to allow for the Heresy to have taken place and unleash the GRIMDARK that we know today.
 * Rogue Trader didn't have the Chaos Gods, either.

The Tyranids are fleeing from more Necrons
Not all the Necrons stayed in the Galaxy, some left those millions of years ago while the others were fighting the wars (maybe they wanted to slaughter everything, maybe their C'Tan wanted to escape the in-fighting, maybe the ones that stayed in the Milky Way Galaxy drew the short stick), and now, they are herding the greatest amalgamation of life they know of into a place they knew they had a foothold (not knowing the amount of decay their brethren suffered from).
 * Yep, because you're totally able to herd an entire species of unstoppable biokillers into another galaxy if you're looking for a foothold. To elaborate: if they're able to scare away the 'Nids, why would they need a foothold? And if they need a foothold, how can they scare away the 'Nids – if they could they wouldn't need a foothold, and if they couldn't they couldn't scare away the Tyrannids.

The Tyranids are a hyper-advanced Flood form
Gravemind reckons that the Milky Way may be a problematic area, what with the Halo's and all, so he takes a Forerunner ship, manages to take control of the cryo pods, and launches a few Flood towards another galaxy. Flood devour all biomass in this galaxy. Repeat for a while, all the time becoming more advanced (it only took a short while for the Flood to become Pure Forms, imagine what could happen in so many years.) They are now advanced enough to not need to take over a hosts body. They remember a command that Gravemind implanted in them (take over the Milky Way unless I tell you otherwise), and begin a mass rush at the Milky Way. Also, those Hive fleets look a lot like tentacles. The reason that no Covenant remain is because they were the first ones destroyed when the Imperium took on its "Kill all aliens" doctrine. Ditto the Halo's.

The Horus Heresy went according to the Emperor's plans.
First of, Horus was supposed to betray the Emperor. Either the Emperor chose him, because he knew Horus would have breakdown once he's put under too much pressure and switch alligence, or because he mentally conditioned Horus to join Chaos when given the occassion. Why? Because the Emperor did intend to become a god from the start. The Imperial Truth was there to eradicate belief in other gods, not because it would weaken the Chaos Gods, but because people would turn to the immortal guy with awesome powers, once they learned there isn't anything else to believe in. Then the Emperor needs somebody to "kill" him, so that he doesn't have to contradict himself when more and more people start insisting he's a god.

Cain actually did everything he is given credit for, including killing Khornate Space Marines in hand-to-hand
Bear in mind, Cain is credited with single-handedly killing two hive tyrants by the people who the books say did the actual killing.

SOYLENS VERIDIANS IS PEOPLE!!!!!!!
Sorry... couldn't resist...
 * The sad thing is, in this 'verse, that'd probably count as genuine virtue... it is recycling, after all. The corpses of all those killed for heresy have to go somewhere after all.

GW's denial of the Squats is just a cover-up of the fact that they'll be the next army.
Please?

Case-in-point, the new model you get with a subscription to White Dwarf is clearly a dwarf with a servo-arm and a freaking space helmet on the ground next to him. It's a Squat.
 * Discussions on that model point at it just being a Mythology Gag, but you never know...

The Tau are GW's second attempt at Cyberpunk Dwarves

 * "hah!" i hear you laugh, "hah! but they're blue! they can't be dwarves! and they've already scrapped the 40K dwarves anyway!" i've been laughed at before, but if you'll just listen just a minute...
 * Dwarves:
 * In Fantasy, Dwarves are more Human than Orks, Elves are more Human than Dwarves, and Humans are more Human than Elves... in 40K, Tau are more Human than Orkz, Eldar are more Human than Tau, and Humans are (kinda) more Human than Eldar.
 * To expand on that, Elves/Eldar are lighter framed humans, Orks/Orkz are big, green, muscley, monstrous humans. Dwarves are midget, massively beardy humans, Tau are slightly shorter, blue, cloven footed humans - i.e similar to enough to humans to see a resemblance, but too dissimilar to pass for each other.
 * Dwarves tend towards technology, Elves tend towards magic. Tau tend towards technology, Eldar tend towards using The Warp/Souls.
 * Tau in fact have no psykers, as their rave has almost no connection to the warp. Similarly, Dwarves have no mages, as their race is inept in casting spells. However, dwarves do have the ability to forge magic runes, an ability the Tau lack.
 * Cyberpunk
 * We're looking at a perfect society, as far as we know, courtesy of a ruling upper class, with no known crime, and they're divided into factions where interbreeding is forbidden.
 * They use mechas and technological implants to improve their combat abilities.
 * They had the technology to leave the planet as soon as the warp storms surrounding them disappeared. how could they know that there was anywhere to explore? why, on having failed attempts, did they continue to progress their technology to the point where they're equipped for space battles? did they know when the Warp storms would clear, allowing themselves to perfect the technology at the perfect time to use it? or did the Ethereals create the storms on purpose to allow them to perfect their fighting machines?
 * Somehow, in just 2000 years, the Ethereals got them from human technology ca. 10,000 BCE to using technology that man isn't using 50 THOUSAND years later. admittedly, man is using some technology that the tau aren't, like teleporters, and in the years of intraspecies war, the Tau that would form the Earth Caste managed to build cities and invent blackpowder weapons, but still...
 * Somehow, in just 2000 years, the Ethereals got them from human civilisation ca. 10,000 BCE to something that humans have never reached (despite previously showing same warlike tendencies between tribes)
 * We only have the Ethereals word that they're the same race. sure, they look almost the same, but despite a worldwide war, they managed to appear from nowhere to stop it. Who the hell are they? is one of the above theories right about them being eldar/necron/whatever?
 * Am I just going mad, or does this make sense to people?
 * I agree that the Tau have essentially filled the "Space Dwarf" niche left after the extermination of the Squats. But a few notes:
 * Tau technology was much more advanced than "10,000 B.C.E." when the ethereals showed up. The codex specifically describes them as using black powder weapons. In addition, the Tau's swift rate of scientific and technological development is perfectly plausible, given what humans have accomplished. The Dark Age of Technology was much more advanced than anything the Tau have accomplished. Humanity is currently less advanced than the Tau due to the Age of Strife destroying most of what they had developed and the Age of the Imperium being marked by stagnation and a dogmatic Adeptus Mechnanicus whose idea of "research" is locating lost technology, and who regard developing new technology as heresy. Of course the scientfically-minded Tau have passed by humanity.
 * Warp storms exist within the warp only, they don't spill over into realspace (That's a warp rift, like the Eye of Terror or the Maelstrom). So they didn't prevent the Tau from using any space travel technology that they developed, but instead prevented other races (notably the Imperium and the Orks) from wiping the Tau out before they had developed a small stellar empire. These particular warp storms protected the Tau, the didn't hinder them in any way. (Which opens up WMG of its own...)
 * The recent introduction of the Demiurg to the tau army simultaneously both josses and confirms this theory.

Doom Rider was once Richard Pryor
He does cocaine & his head is on fire. Obvious, really.

The real name of the Emperor? Kal-El, of Krypton.
Superman decided that humanity's defences were inadequate, so he set about unifying them under his rule. Fast forward to the 41st Millenium, and his vision has Gone Horribly Wrong.
 * Just a few problems with that. Superman was an alien and knew it, so why would he be anti-alien? Also, did Horus strike him down with a kryptonite sword?
 * Superman is also vulnerable to magic--not in the same way as to kryptonite, just insofar as it bypasses his invulnerability. So maybe it's a magic sword, however you define "magic" in this continuity.
 * As for the anti-alien sentiment, it could be due to just how utterly horrific the world turned out to be. Even Kal-El couldn't fight the grim darkness.

The real name of the Emperor? Dio Brando.
Void Dragon: "I have always existed, I have drunk the stars themselves, you cannot defeat me pitiful little crea-" Emporer: "Za Warudo!" Void Dragon (two miles under the surface of Mars): "-ture. Wait? What the hell?!"
 * Think about it. He can kick the ass of every other god in the setting because he has "Za Warudo!"

The Emperor is an agent, perhaps unwitting, of the Chaos gods.
What does it say at the beginning of all the novels: "It is the 41st millennium. For more than a hundred centuries the Emperor has sat immobile on the Golden Throne of Earth. He is the master of mankind by the will of the gods. [Emphasis added.]"

Which gods could these be? The Imperium worships only the Emperor himself. Gork and Mork, the Ork deities? The surviving Eldar gods? Cegorach, who is in hiding? Isha, who is in captivity? Khaine, who is in pieces? Or perhaps the C'tan, who have slept since before humanity existed, and only awoke recently? None of these beings seem to be credible candidates. No, it can only be the Chaos gods, who have clearly been deeply interested in the affairs of the Imperium since its founding. The only question is why they want the Emperor on the throne of Terra, and whether the Emperor knows that he is their agent.
 * I always tought that the 'gods' who endorsed the emperor were humanity's own warp entities, like Zeus or Thor or possibly Ra. They got consumed by Chaos a long time ago (they only had energy from one planet of sentients, and they were so many of them that they didn't have enough power to resist) but were able to give their power to the Emperor before they were fully consumed. But since there's no canon evidence for such a thing, that's another WMG entirely...
 * That doesn't really work, because the Emperor is supposed to have been around since prehistoric times, which means before any of those beings were worshiped, or even dreamed up. But consider this: who puts that inscription about the Emperor at the beginning of all the Warhammer 40K novels? The publisher, obviously. And who is the publisher? The Black Library. And what is the Black Library? It is the repository of all the information the Eldar have collected on Chaos over the millennia. So why are all these stories about the Imperium coming out of an archive that's supposed to be about Chaos? Because the whole Imperium unwittingly serves Chaos, because the Emperor is an agent of Chaos. It's all some big Xanatos Gambit, probably by Tzeentch.
 * Tartar Sauce! And it was a good theory too. What about the Great Mother and the Great Horned One? They can't be aspects of Slaanesh then, as s/he was born during the Fall of the Eldar, which was thousands of years after the Emperor's birth. Sorry, grasping at straws here.

The Emperor is dead.
Has been for thousands of years. The Golden Throne could keep him going only so long, but he kicked the bucket ages ago. Or maybe he's been dead since the Horus Heresy, and the life-support system is just a myth that the High Lords of Terra cooked up with the leaders of the Mechanicum so as not to have humanity getting driven down to suicide.
 * There's a reason that the followers of Chaos call him the "Corpse-Emperor" or "Corpse-God".
 * Then explain how the light of the Astronomican is still open for the psykers to use to get through the Warp.
 * It's being powered by all the psykers who get sacrificed to it every day. The Imperium just claims that it's still being directed by the Emperor in some way as part of the propaganda that he's still alive.

Slaanesh did not kill the Eldar gods. He is the Eldar gods.
Consider: warp entities, including gods, are created by the worship of living beings in the materium. The Eldar created Slaanesh because, whatever lip-service they paid to Asuryan, Vaul, and the others, by the way they lived, they were actually serving Slaanesh. So Asuryan and the others were transformed into Slaanesh. The Eldar experienced this as Slaanesh "devouring" their gods, because that is how it would have seemed: the old gods were being absorbed into the new one. The warp storms the preceded Slaanesh' birth were, metaphorically speaking, the chrysalis by which the bulk of the Eldar pantheon metamorphosed into Slaanesh.

The reason Khaine, Cegorach, and Isha survived is that they were the only remaining of the old Eldar deities who were still receiving sincere worship anymore, so they were able to remain distinct from Slaanesh.

Everybody is the Emperor in his life support
It's addictive.

== At some point before the Emperor's reign, Earth faced a cataclysm that destroyed much of humanity's cultural heritage - the biggest surviving cultural forces were the Catholic church and heavy metal. == Thus all the gratuitous Latin, the ideology of "burning heretics" and Rule Of Brutal-based everything. This is probably Dethklok's fault somehow.
 * Don't forget TV Tropes, to explain its troperrificness.

The next edition will be distinguished, not by things getting better or worse, but by things getting sillier.
The setting's so over the top that it's ripe for black comedy anyway.

The missing Primarchs are still alive and in hiding.
All twenty Primarchs participate in the Great Crusade, and the records of II and XI were deleted after the Heresy. Their respective Legions were annihilated in the fighting, leaving only the two Primarchs around. Realizing that the Galaxy was going to get worse before it got better, they decided to cut their losses and hang up their helmets for a while. For the past ten thousand years they've been silently waiting for the proper time to re-emerge.
 * The histories of the legion II and XI were deleted during the Great Crusade. Even the Primarch's considered it a taboo to even mention them. Little is known about their fate, save that they are referred to as the "forgotten" and the "purged". This could potentially refer to two separate events. The only other bit of information is a subtle reference from Leman Russ immediately after the destruction of Prospero; he implied that the Emperor ordering a Legion to fight against another legion was not "unprecedented".

Ghazgkull and Yarrick will team up.
To destroy a chaos invasion. Why? Well, it'd be awesome, but the both of the them will be trapped together for a while and realize that they actually like each other a lot, and that they both could work together to destroy an enemy that they both hate. In fact they'll both show up with a giant fleet and in fact will destroy them with their sheer coolness when they're really needed, maybe in the final battle.

The Emperor is/was several people, possibly an entire legacy of clones.
Genetic experiments have existed for a lot longer than since the creation of the primarchs and so has he. Some group of genetic engineers on Ancient Terra managed to create a perfect warrior and leader figure, but immortality was not in their reach. So they used him to rise to power while always replacing the Emperor with a new one when he died, keeping him (and them) eternally in power. But after Horus put him in a coma, the scheme backfired as they realised the religion they created to help them maintain their controll over Mankind would not take kindly to an "impostor" replacement they produced, so they had to disband and keep their secret.

The Emperor is indirectly responsible for almost all Magical Girl warriors ever.
We know that The Emperor had to throw out his compassion away so he could kill Horus. The Star Child theory that exists in-universe tells us that his compassion can bond to itself in the form of a new facet of The Emperor's personality comparable to the Omnissiah, different, but still part of the greater being.

Now consider what would happen if his compassion could make simple decisions. It would probably want to get as far away from the GRIM DARK 41st millennium where its favorite son had just been killed by his own hand. The Emperor has been stated to have time warp powers, and an aspect of him that did not have to do anything like powering the astronomicon could possibly muster enough psychic power to achieve true time travel.

The compassion aspect would travel to the late first/early third millennium, where there are far fewer horrors that imperil humanity. It would be very weak and could even be scattered over the planes of existence, like an egg that broke and spilled on the floor (in a pan-dimensional sense). The first instinct upon arrival would be survival. It would go about this by attaching to human hosts in whatever form it could, becoming various transformation trinkets in a manner akin to soul binding.

The hosts it would seek out would be young, caring, and female. Why female? Because compassion, love and other "soft" emotions are more feminine than masculine. The Emperor, the dominant aspect and with more than a hint of War-God ( Great Crusade and all ), is masculine. The Omnissiah, the aspect of knowledge and machinery ( and by proxy the the war aspect, war-machines ) is not solidly referenced to by gender ( I cannot recall the Omnissiah being referred to as a he with any regularity ). The most war-oriented the compassion aspect can be is as either the supply lines that feed the conflict, the bonds of warrior brothers, or the healing and recovery from after war.

During the first meeting with the hosts the aspect would involve an infodump explaining things the the host. The reason they all get different backstorys is because the trauma of traveling so far through time has rendered it a crippled with no clear idea of what happened, but its stronger connection to the War/Main aspect gives it general sense of directive to oppose Chaos and safeguard humanity.

The form Chaos takes in this time frame to threaten man is small time Daemon lords trying to take a few billion souls to jump-start there carriers. The first choice for the aspect would be to fight would be daemons serving Khorne, god of hate.

All this time attached to the host, the aspect will amplify the power of love to insane levels to fuel the hosts powers to fight anti-lulz. When the host is in civilian mode the aspect will squirrel away psychic compassion resonance to send to the future for the Star Child.
 * At the very least, this theory certainly explains the reasoning behind Nanoha Takamachi's insane amount of firepower and mentality...
 * Didn't Sailor Moon end with her destroying Chaos?
 * She "put it back where it belonged, back into the hearts of humans."
 * That. Explains. Everything...!
 * "In the name of the Moon God-Emperor of mankind I punish you!
 * Puella Magi Madoka Magica is one of the Magical Girl dimensions closest to the actual 40k universe.

The Star child is Mr. Rogers from Mister Rogers' Neighborhood.
He is so nice that he can de-crapify ANYTHING.

The Illuminati exist, and are tragically almost-right about the Star Child.
The Illuminati are, in the same old background that introduced the Star Child, a group of people who managed to throw off Daemonic possession by sheer will. Unfortunately, Tzeentch had a plan for this, and made sure his Daemons left behind simple suggestions buried deep in their former hosts' minds. They plan a mass sacrifice of the Star Child's champions to pull together the scattered aspects of the Emperor's will with his long-discarded humanity dominant, reborn in a (super)human body. This would work...to the great advantage of Chaos. Even with the power of a popular god as well as the greatest of all psykers, his attention would be far more limited by cohesive identity and incarnate consciousness. The most urgent of prayers would go unanswered and the hearts and minds of innumerable faithful lie unshielded, to be claimed by the Ruinous Powers. Just As Planned.

The Star Child is David Bowman
The name makes it obvious, people!

Chaos Space Marines infected with the Obliterator virus will actually the good guys (whatever "good" that means in this universe).
My reasoning for this theory? Well, Obliterators are basically living guns, and as our God Zardoz has said, THE GUN IS GOOD. They (like most Chaos Space Marines, or for that matter most Space Marines, or most Chaos forces, and in fact most people in this 'verse) like to use most of their time to GO FORTH, AND KILL. The true ultimate evil of Warhammer 40,000 will be the Emperor's Children legion of Chaos Space Marines. In a future update of the fluff, their forces will be enhanced with a Slaaneshi varient of the Obliterator virus, and will be the embodiment of Zardoz's concept of Evil.

Chaos of Ultraman Cosmos and the Chaos of Warhammer 40000 are one and the same.
Both corruptive, both coming from who knows where, both having a love of destruction, and both will mean the end of sentient life if they win. Anyone want to add summat?

There is going to be another chaos god.
They have been building up to it. The grim darkest W40k ever got.

Emperor help us, when the Chaugle, God of Chairs arrives. CHAIRS FOR THE CHAIR GOD, THRONES FOR THE THRONE THRONE!
 * And he was Chairface Chippendale before his ascension.
 * They already did it. Malal(now Malice) is back. In pog form.
 * Clearly, the next army list will be the missing primarchs' legions, corrupted into the most grimdark faction in the galaxy. The Pog Marines shall rise...

The Tyranids are running from the Chaos god of Hunger
Trillions of monsters with a powerful psychic Hive Mind with insatiable hunger are bound to start something in the warp. They made an eye of terror in their home galaxy, and they are the dark eldar to the hunger god's Slaanesh. There will be a faction of non-hungry, repentant Tyranids to act as a normal eldar counterpart, somehow having a seperate hive mind. They will live in giant synapse creatures that are their version of craftworlds.
 * Non-hungry Tyranids?!?! Holy crap, even Brighthammer 40000 didn't go that far!

The Warhammer 40k MMO shall focus on the Eldar
It will be called War of CraftWorld
 * Or "Craftworld of War" or "War of Craftworld."

Games Workshop are secretly worshippers of the Chaos Gods, and their line of toy soldiers is an evil Chaos plot by Tzeentch to get us all addicted for life.
I mean, what with crack being cheaper and all...
 * Or they are a front organiation for Chaos, as they control both settings they are active in...

Warhammer 40k happens in Real Life's version of the Warp.
Think about it.

Sheriff Ed Tom Bell is one of the Lost Primarchs
After the Ruinous Powers snatched the young Primarchs from the Emperor on Terra and scattered them across the Galaxy, one of the two that were never found again was Ed Tom. He had been launched back in time to twentieth-century Texas. There, he was found and adopted by a normal human, a la Superman. But the trauma of the journey stunted his growth, so he only became a man of normal stature rather than reaching the imposing size of a normal Primarch, and he aged as a normal man, as well.

His first dream (which he doesn't remember well) is of trying to find his father to get some money, which Ed Tom thinks he lost. The second is of his father leaving him alone in the cold to go ahead and start a fire.

The "father" that Ed Tom sees in both dreams, the man he knows as his father, found and adopted the Ed Tom when he found him as a baby, alone and abandoned, in the Texas desert. The dreams are not really about this man, however. They are about Ed Tom's true father, the God-Emperor of mankind.

The first dream is fragmentary and partially forgotten because Ed Tom was spirited away as an infant, and so had no knowledge of who or what he was, but his latent Psyker abilities have painted him an incomplete picture of this. He knows he has a greater destiny than to be a sheriff in rural Texas. The "money" that his father is going to give him is his rightful destiny as one of the sons of the Emperor and leader of a legion of Space Marines, defending Mankind and building the Imperium. He has the fundamental feeling that he has lost this, which he has, by virtue of being cast back in time and stripped of most of his power.

In the second dream, his father passes him by on a cold mountain pass without pausing to speak, in order to go ahead and light a fire in "all that cold and all that dark." This is about the God Emperor's mission to take the reigns of leadership over Mankind, in order to light a fire of inspiration and hope in the cold, dark distance of the far future. But because of the upset in time, Ed Tom can only stay behind and watch as he goes on ahead. Because Ed Tom was meant to be -and should be- immortal and able to simply take The Slow Path to join the Emperor and his Brother Primarchs in the Great Crusade, he has a moment of hope that whenever he gets there, his father will be waiting. But the same Psyker abilities that fill him in on the past break that hope by giving him the premonition of Horus' betrayal, and his own knowledge reminds him that he is cruelly mortal. And so he wakes up.

It is the knowledge that despite being made and nurtured by the hand of the Emperor himself and bred for the sole purpose of being an immortal, invincible guardian of mankind, he has by a whim of fate been consigned to live and die a mortal man, and that in the face of the infinite, universe-shattering threats the universe holds, he cannot even contend with the evils created by humanity itself that drives him to despair and a defeated retirement.

Warhammer 40k is set in the Old World of Darkness
The reasons? No reason, I just thought this would make everything in the 40k universe worse.
 * Hey, remember what was originally going to be the backstory of the World of Darkness? I mean the Emperor is totally a Solar Exalt.
 * Tyranids are the Wyrm. Necrons are Wraithes and Sidereals. The Mechanical God is the Weaver. Psykers are Mages. The Inquisition started with the Hunters. Chaos are the Yozi. Orks are from the Wyld. And the Tau are geniuses.
 * The Dark Eldar curse is actually a derivative of the curse of Caine. Commoragh is the Enoch of the new millenium.
 * The Warp is the Umbra, almost completely dominated by the Wyrm. Each chaos god is a head of the Triatic Wyrm, with Khorne being the Beast of War, Slaanesh being the Eater of Souls, and Nurgle being the Defiler Wyrm. Tzeentch is the last remnant of the Weaver.
 * Chaos Spawn are actually Formori in service of the Wyrm. Daemon Princes are what happens when one of them ascends to Incarna level. Rank and file Daemons are simply very powerful Banes.
 * The Blood Angels are the remnants of the vampires, who by now are such thin bloods that all that remains of their curse is bloodlust and frenzy.
 * Necrons in their early editions are spectres, bound permanently to the fetters of their bodies, and the C'Tan are Neverborn. In the new edition, Necrons are still wraiths, but have somehow found a way to shatter and imprison the Neverborn to their service. Flayed Ones and Destroyers are still Spectres.
 * Inquisitors are Hunters. The Wayward creed seems to have taken over the order.
 * And finally, the Tech Priests are the last remains of the Technocracy.

The Orks have realized that they can bend reality.
Case in point: In the 41st Millenium, There Is Only War.

The Imperium of Man (as we know it) will roll over and die.
Tragedy will befall the Emperor, shaking the very foundations of the Imperium. Admist the panic and confusion, humanity will be divided. The Imperial Guard will break down and scatter. The various Space Marine chapters and the Inquisition will become separate kingdoms, each laying claim to a fraction of what was once the empire. And needless to say, the ranks of the Chaos cultists will grow tenfolds.
 * That is clearly implied in every single square centimeter of the Warhammer 40k Verse. It's not really that wild.
 * The canon is wilder than the guess...for as long as some faint heroism remains in the heart of Mankind, the Imperium endures.

The Necrons were meant to destroy the Tyranids.
Self-explanatory. The Necrons are merely galactic pest control.
 * Orks were also made to fight the Necrons.
 * She swallowed the spider to kill the fly...

The Imperial Guard is a highly competent Badass Army that not only wins the vast majority of its battles, but rarely takes any casualties in the process.
The Imperial Guard has by far the longest-ranged artillery of any army in the game, along with the best metal boxes, so of course their standard tactic is going to be to blow away their enemies with cannons and ballistic rockets from miles away. The tabletop battles you see involving the Guard? Those are the rare occasions where an enemy got close enough to shoot back. Of course, if an enemy does get close enough to shoot back, or, even worse, launch melee attacks, bad day for the Guard. Still, those would be the only occasions where the Guard would take any serious casualties. Also, all those novels about the badassery of the Imperial Guard.
 * Isn't avoiding melee battles and shooting the shit out of your enemies with superior firepower the Tau's tactic?
 * Long-range artillery doesn't suffice when your enemy can freaking teleport. Or when their numbers are endless. Or when they are utterly invincible. Or when...well, you get the picture.
 * How many of the teleporters can jump inside the range on an ICBM? Also, numbers don't really help against artillery, since the space you have to squeeze those numbers into is finite. The more guys you have bunched up in the blast radius of the shell, the more the shell will kill. And none of the enemies are actually totally invincible, even if they seem that way some of the time.
 * I thought this was pretty much canon. Most wars are decided by the imperial navy showing up and nuking everything from orbit. Most of the rest are decided by the guard showing up with ridiculous amounts of tanks and blowing everything up from over the horizon. Only when important stuff like ancient cathedrals or titan forges is in risk of becoming collateral damage do the dudes with lasguns show up.

Apple is the Adeptus Mechanicus.
Okay, so every new device they release is simpler to use and harder to work on (Only apple personnel can do so, otherwise the warranty is voided) Eventually, apple will drive all other device makes into a corner while their interfaces become simpler and simpler yet impossible for anyone other than trained apple technicians to work on. To perpetuate their now great power over the people, apple engineers will mythologize their devices, alluding to supernatural components in their function. Their customers, who already wait in line to buy ridonkulously overpriced versions of fairly conventional technology readily available elsewhere at a far cheaper price, will be utterly taken in by this and venerate their words, at this point they will start affecting themselves as priests and innovation will slow down to a crawl as the faithful grow to venerate their apple devices with fanatical fervor. At this point, the few remaining PC crowd who actually work on their own machines will be rounded up as heretics and executed in a bloody inquisition, and apple's dominance of the technology sector will be complete. Steve Jobs will be deified as the Machine God and in time, the secrets to innovation will be lost and all new products will be copied from old patterns.
 * I thought it was PCs that required prayer to work?
 * Ba dum tish.

The Adeptus Mechanicus is Microsoft
In counterpoint to the above, the hallmark of Apple OS is user friendliness, sometimes to the exclusion of functionality. Windows, by contrast, tends to be more functional but less user friendly. Tech in 40K is shown to be capable of performing a wide range of of functions, but is almost impossible to use without being inducted into a secretive brotherhood of tech-savants, prone to break down for no discernable reason save the whim of some angry tech-god.

The Tyranids are causing the Necrons to awaken.
The Necrons originally went to sleep because they had been so effective in ridding the galaxy of life that there wasn't enough life left for their C'tan masters to feed on anymore. So they went to sleep to give the population of the galaxy time to recover. In the meantime, the Tyranids have been approaching, bringing with them the combined biomass of several galaxies that they had already consumed. Sensing all that life approaching, the Necrons have begun to awaken. Of course, so far only the Tyranid vanguard has arrived, so only a handful of Necrons have awoken. When the hive fleets start showing up in force, all the Necrons will awaken. And then it will be on like Donkey Kong.

The Orks are in control of everyting.
Subconsiously of course but think about it. the orks think Yarrick had an evil eye and then he got one. they belive that war is the end of everything, the orks rule the entire galxey though their beliefs.

The Golden Throne is working perfectly fine.
Its purpose isn't just to sustain the Emperor -- it's also been slowly repairing his body. It's taken a while, but it's making good progress. The "malfunctions" are certain devices shutting down as their work is done.
 * Or perhaps it's meant to let him decay. Sure, Magnus busted its Webway-control functions, but the Emperor could have left good enough instructions to keep up its life-support functions. That wasn't his plan. If he was ever disabled and forced to fall back on the A God Am I plan, it was meant to sustain him as a single embodied mind only long enough to build up the necessary worship to face the Chaos Powers as their equal. It is merely the egg from which the true Emperor-God will hatch.

Warhammer 40k is not the future of Warhammer.
It's the past.
 * What? I thought it was common knowledge that Warhammer Fantasy took place on a feudal world.
 * Nonsense. In the future of Warhammer 40k, something happens that wipes out the Necrons and the Tyranids, while reducing the scale of the conflict to one world.

The Chaos Gods aren't making the setting grimdark.
The Chaos Gods are the embodiments of both positive and negative emotions. Whichever is more prevalent in the galaxy at the time determines their being good or evil.
 * So, the dark universe makes them evil... but their evil makes the universe worse... It's positive feedback!

The various gods were once mortals... in the Team Fortress 2 universe.
Expanded from the Team Fortress 2 WMG:


 * 1) Scout: Gork/Mork (the smart one)
 * 2) Soldier: Khorne
 * 3) Pyro: Malal
 * 4) Heavy: Gork/Mork (the violent one)
 * 5) Demoman: Slaanesh
 * 6) Engineer: Void Dragon
 * 7) Medic: Nurgle
 * 8) Sniper: Khaine
 * 9) Spy: Tzeench
 * 10) Helen: Deceiver
 * 11) Saxton Hale: The God-Emperor or CIAPHAS CAIN, HERO OF THE IMPERIUM!

The Machine Cults rituals and prayers work for two reasons
Part of in a mnemonic memorisation device. Works especially good for little things like 'The Litany of True Aiming' and helps the actions become automatic, even under high stress conditions. The second is that as humanity is slowly evolving towards and all psychic race they're developing something akin to the latent field that allows Ork technology to work in strange and unusual ways (such as paint colour affecting the speed of their vehicles). The Mechanicum has spent so long convincing their rituals are necessary humanity's growing psychic abilities actively contribute to the success. As a result when the rituals aren't done there is a distinct drop in effectiveness/efficiency which only re-enforces the belief. The success rate of performing Percussive Maintenance (canonically a measure of aptitude for becoming a tech-priest) is indicative of a person's ability to focus this effect.
 * The second part here is nearly-canon...humans and other races with an average-to-better Warp presence influence the Warp whether or not they have obvious Psychic Powers. There is one main difference between the Orks and the Mechannicum, though--the Orks work directly through a field of joined will, Gork and Mork being fairly minor in comparison; the faith of the Mechanicum, and others' belief in them, is focused through the semi-autonomous entity of the Machine-God, partly joined with the Emperor's will, and the machine-spirits it spawns.

Almost every human soul is absorbed by the Emperor upon death
Canon states that the Emperor was basically the manifestation of "thousands" of psykers who committed mass suicide. He is also implied to be greater than the four primary Chaos gods combined. It seems to follow that only a few thousand psykers would need to concentrate to wipe out the gods of Chaos, however we all know this isn't true. Why is the Emperor so powerful? Because being absorbed by him is the "default" setting of the human soul after death. While only a few thousand psykers may not be a match for the Chaos pantheon, the collective souls of every human being over millennia almost certainly is. Only people who directly worship a Chaos deity fail to be absorbed by the Emperor.
 * This adds another layer to his reasoning behind spreading the "Imperial Truth." He ensures that people will stop worshiping (and empowering) false/evil gods.
 * Furthermore, it adds a layer of Fridge Brilliance to why the Emperor is such a magnificent, godly figure. . . but also kind of a dick. He is humanity made person, with all of our greatness, and all of our flaws.
 * I award you sir, the internet.

The Imperium is actually run by an old man in a shack.
The High Lords of Terra are merely figureheads.

FATAL actually takes place on some Emperor-forgotten backwater of a planet ruled by Slaanesh.
I haven't played the game, but it does sound like the above would fit. Explains the whole "medieval Europe, only with no Christianity" thing, and the general screwed-up-ness, amongst other things.

At some point, the Imperium will stumble across them, and an Exterminatus will be carried out a few minutes later.

The Inquisition are actually Daleks.
The order to kill a planet is called Exterminatus, for goodness' sake!

The Space Wolves will kill the Emperor
In Norse mythology, the Fenris wolf was prophecies to kill the Allfather - and the Space Wolves refer to the Emperor as the Allfather The Space Wolves will learn that the Golden Throne prevents the Emperor from being reborn, and will attack Holy Terra, destroying what remains of the Golden Throne and Emperor's body. And the Emperor will be reborn. But the Ecclesiarchy will not accept that the Emperor has been reborn, and, with conflicting reports that the Space Wolves have become traitors, the Imperium will be plunged into a new civil war.

Following on the "Tau=Necrontyr" theory, the rise of the Tau is the result of an intervention of their (and the Necrons') former gods
Okay, kind of a stretch, but here's how it works. We do know that Eldar and Ork have warp gods. For all we know, Tau (and maybe, by extension, the Necrons) don't have a warp signature, but maybe that doesn't mean they don't have an impact on the population of the warp. Back when they were still the Necrontyr, the Necrons may certainly have gods of their own, who as a result of their worshipping appeared in the warp. However, when the Necrontyr decided to join the C'Tan's side, those gods then only got worshipped by the very, VERY small Necrontyr population of a backwater planet who didn't want to become metal like the rest of their species, and who would later become the Tau. Because the link between the Necrons and their gods broke after their transformation, those gods couldn't do anything but to protect the proto-Tau from their former brethen. Fastforward a few million years, and those gods, severely weakened, could however still feel that their lost children were beginning to awake. So, to make some sort of compensation for the rebirth of the Necrons, the gods contacted the Tau which still had a tiny spark of warp signature, and turned them into the Ethereals. Then, to be sure they wouldn't fall to the same extremities than the Necrons, they made them spread an ideology that was putting an emphasis on sacrificing one's fate for the good of all the other living beings (the Necrontyr, after all, fell because of their selfish desire to increase their life expectancy, even at the cost of the rest of the galaxy). Guided unknowingly by their former gods, the Tau could evolve beyond the stone age and became the booming high-technological empire we know today.

It's going to get much worse, because...
The next Chaos god is going to be the Yaoi God, created from a mad Yaoi Fangirl! Then, they would rename the taglines as "... in the grim darkness of the far future there is only war YAOI!" And then, they would add units like Uke Space Marines, and something like that.
 * Eh, already covered. That's a tiny little aspect of Slaanesh.
 * All Space Marines are Semes, it's the Imperial Guard who are the Ukes (except for Gaunt, and Cain).
 * And Yarrick.
 * Great, the goddess of chaos write Harry/Ron and Aku Roku fics in her spare time.
 * Where else do you find such a concentration of Hurt Comfort Fic, Rape Is Love, Foe Yay, and other terribly Slaaneshi tropes?
 * Give me five minutes on Google, I'll find something.
 * BEHOLD, THIS EXISTS!!!

40K is secretly the most Anvilicious work. EVER.
Despite the presence of at least two definite Space Whale Aesops (the Eldar backstory and Chaos worshippers), there are some quite sensible ones:
 * The Imperium: Don't be an overly paranoid racist who gets angry at anyone different or you'll be making enemies faster than you could pick up a gun.
 * Also, the AI Is a Crapshoot angle in their backstory.
 * There's also one about "Well Done, Son" Guy: respect your kids or they'll go Oedipus Complex on your ass.
 * Argh. Too tired to think of any more.
 * The Eldar backstory is actually also quite sensible: don't devote yourself to purely hedonist self-indulgent pursuits, or the negative side effects of your actions will ruin your health and your life in the long run.
 * Necrontyr: Don't take loans that sound too good to be true, they probably are and you'll be regretting it for the rest of your life
 * Who cares, when you can live forever!
 * Tau: Just because you think you're in the right and have the moral high ground doesn't mean you are in the right and have the moral high ground; fundamental differences in cultural perspective can make all the difference, and there may be something important that you aren't aware of

The Emperor is a Time Lord
And he's just the most well-known.

Early First Edition was an Alternate Timeline.
The divergence point was very early--instead of fighting a long war where stalemate turned to slow defeat, the Old Ones sacrificed themselves to destroy the C'Tan and all their works, leaving the Slann to inherit their territory and knowledge. This massive attack created the Eye of Terror and scattered the Eldar eons earlier--but it also was strong enough to literally drain the Warp, tearing apart the nascent Chaos Powers and generally weakening supernatural powers--thus, the different tone of the world, in which destiny and belief are far weaker forces. In addition, this meant that the Emperor lacked the power to create the Primarchs to his satisfaction, and was weak enough to gradually fail without combat injuries, eventually needing to be confined to the Golden Throne anyway. The absence of the C'Tan explains why the original Rogue Trader book places the Mechanicus on Earth...without the Dragon, there was no advantage to luring the tech-cults to Mars.

The Tyranids are actually the physical incarnation of The Maw.
The Warhammer Fantasy world can deem itself lucky to only have the Ogres.

The orks used to be much more organised, only the dumb ork class overthrew the smart
Because honestly, it doesn't seem like many orks follow the god of brutal cunning anymore and that guy had to come from somewhere right? So, relatively smart orcs once existed. Than one of the orks discovered smart orks made a funny squish sound when they died. And that was the end of a cunning leadership.
 * Previous editions stated that the Orks were actually created by the Snotlings as a warrior class, before they'd degenerate into the insignificant and almost animalistic grunts they are now. It's much more ambiguous now, as the Old Ones are now considered to be their creators, but maybe the Snotlings were still once the Orks' ruling class.
 * The newest codex mentions both, based on Ork oral histories.

Doom is ancient 40k history
Demons coming from attempts to warp to places? Check. Bad-ass space marine? Check. Lot's of shooty and chainsaw violence? Double check.

WH40K is in the grim darkness the far future of the Terminator franchise
After the nuclear holocaust set in motion by Skynet, John Connor sent human colonies into space to help gather resources from across the galaxy, to help defeat the Terminators. Skynet sent various forces after them to capture and exterminate these humans, but many of them went underground after having lost all contact with the colonist humans, and these became the Necrons. The original Necrontyr went extinct with the war with the Eldar, and the C'Tan literally fled underground since their fighting forces were exhausted, but are re-awakening now that they have a fresh fighting force.

The Void Dragon influenced the creation of Skynet, allowing it control over Skynet, and in turn, allowing Skynet to rise up against humanity. This was all part of a millenia-long, albeit failed, Xanatos Gambit by Void Dragon to have an army that could punish humanity and release it from its prison underneath Mars.

The robot war was the start of the Dark Age of Technology, with the war for survival prompting humanity to begin colonization of space and jumps in technology. The eventual defeat of Skynet's Terminators left humanity in shambles, starting the Age of Strife. All of this is forgotten since the Emperor, the only one who would remember this, decided to suppress this information for the good of humanity; and the Eldar see no ideological difference between the Necrons and the Necrontyr. Also, the Iron Men STC found by Gaunt were the plans for the original Terminators.

The C'tan control over Skynet is what also allows the other C'tan to command Terminators/Necrons, since Skynet no longer exists to facilitate commands to the Termicrons. All the inert and slumbering Tomb Worlds are Termicron colonies on stand-by, waiting for eventual orders.

Blanks and Pariahs
More analysis than WMG, but here goes anyway...the two types of psychic nulls are far more alike in their origins (a symbol scribed in DNA that disrupts the Warp) than their effects. Blanks are effectively a living Gellar Field, diverting warpstuff around them; Pariahs are a sucking hole in the Immaterium, drawing psychic energy inward to annihilate itself, in its passage tracing the negative image of a human warp-soul. This negative image is why, in Nemesis, the mind of Spear the Black Pariah was dimly visible to a psyker he was "sucking". Thus, Blanks are more perfectly immune to Warp powers, while Pariahs are far better at creating terror and, with the aid of Culexus equipment or Spear's unique powers, may throw back energy they have drawn away but has not yet annihilated, transformed to their own indrawing nature.

One of The Emperor's more recent aliases from the perspective of our era is Joshua Norton
Self explanatory. Emperor Norton really was The Emperor, either He was getting impatient, wanted to do a dry run, or was just really, really bored while waiting for the next stage of His Great Plan For Humanity.
 * I've always thought that Joshua Norton was really, really bored after being stranded due to losing his Electronic Thumb...

The Tau actually are the Good Guys
The concentration camps (or whatever they are) are obviously Imperial propaganda (hell, most of the Tau codex is told from the point of view of the Imperium. Devilfish, Manta, Piranha skimmers, Hammerheads, all are Terran fish names given to Tau vehicles by the Imperium), the translation devices given to the Vespid really are just that, translation devices, not mind control devices (for starters, Vespid Strain leaders aren't Fearless, as they would be if mind controlled, and Commander Shadowsun's ability to let any Tau unit or Vespid unit with a strain leader (who has a translator) use her Leadership for Morale checks, as the strain leader would relay what she is saying to his squad), etc etc.
 * Mind you, even if there was some degree of thruth to those rumors, the Tau would still be good guys compared to everyone else...which says a lot.

The Na'vi are Exodite Eldars
Pandora is the Death World they've settled. The Tree of Souls is their Infinity Circuit, which they actively worship as a World Spirit. Oh, and there's no Eywa, just a series of subtle, behind-the-scenes Harlequin interventions...
 * Exodite worlds are Maiden Worlds raised from a dead rock to being a vibrant jungle world and given sentience. I like to think that the world from Daemon World where

Boltguns have been invented...for real.
This. Or this. It fires 25mm High Explosive Shells (boltshell) with a laser guided system and various optics(M.40 Targeter), semi-automatic (usual canon depiction of a boltguns' mechanism). That's right, ladies and gentleman. The madness that is Warhammer 40,000 is one step c retloser to reality! Sleep tight!
 * Oh calm down, we have around 28,000 years left until Horus betrays His Imperial Majesty and things start getting REALLY worse. We'll be long gone by then, even our souls, and the grand galactic war isn't scheduled to really heat up for a while; most of the threats aren't even close to ready to attack us. I mean, has Slaanesh even been born yet?

The Old Ones Are Just Hiding and will return to save the day...
...for themselves, of course, since this is Warhammer 40k. They'll come back and decide that if they want a livable galaxy, everything's going to need to go. Yet another front is added to the war and the status quo remains more or less exactly the same, aside from shuffling around of who owns what planet.

Khorne's change in method was the result of Slaanesh's "ascension" and a helpful nudge by Tzeentch.
For a few issues, Khorne was certainly the God of War, but he was honorable nonetheless. His followers sought bloodshed in honorable battle but would leave women and children unmolested (unless they tried to fight back, of course.) Of course, that changed rather abruptly to "[not caring] from whom the blood flows, so long as it does." Given the bizarre nature of time flow as compared between the Warp and realspace, this belated change of heart could have been the earliest realspace manifestation of Khorne's reaction to Slaanesh, to him the most despised of the rival Chaos Gods (of course, Tzentch may have pointed this out as a wise course of action, Khorne's never been known for subtlety.) Although Khorne loses some personal honor by slaughtering everything that moves in a rather spectacular fashion, he denies Slaaneshi daemons their "enjoyment" and increases the blood flow. And even to a mortal suffering a Chaotic incursion - would your soul rather be just euthanized down quickly if not cleanly, or tortured and squick-orgied out of existence along with your partner and children forever and ever?

Khorne's change in method is parallel to the general state of the world going to crap.
Since Chaos is but a reflection of our hopes and desires, and since he was specifically born from humans, Khorne's Motive Decay and motto of "BLOOD FOR THE BLOOD GOD!" is actually the Imperium's Motive Decay and motto of "HERESY! *BLAM*". His earlier Proud Warrior Race Guy ways were a throwback to the golden age of mankind, but those days are long gone now, and in the Time of Ending both of them have turned Ax Crazy...

The Necrons and Tyranids aren't as unstoppable as they're hyped up to be.
Yes, Necrons are unkillable death machines... but their numbers are static (even if currently unknown). They also seem to lack the ability to get anywhere NEW in a hurry (Though they can move amongst their own areas swiftly). They don't pose a threat to the Imperium because the Humans and Orks(A race specifically designed to kill Necrons) reproduce faster than the Necrons could ever hope to kill them. The end result would be Necrons being as effective at Killing humanity through their genocide campaign as a respawning Mosquito is at killing a human through blood drain.

And while a lot of ado is mentioned about the Tyranids theoretically having the power of the biomass in the Galaxy, the first and second most numerous collections of Biomass (Orcs and Humans) aren't restricted to just organic matter for their firepower. In the end, the Tyranids will run out of Biomass it can access before the residents of the Galaxy run out of Bullets, Plasma, Tanks, Starships, Powered Armor, Bolters, and lasgun charges. The Tyranids will go SPLAT like bugs on a windshield against the Might of the Imperium or the Orkish WAAAGHHH! At that point, they'll become like Orks in that they're scattered about the galaxy trying to eat enough to rebuild their swarms (Just as the spores of defeated orcs try to regrow)... but they, unlike the orks, don't terraform the land around them to be more hospitable to their kind (If I remember, Orks grow all sorts of Squiggoths and Orkish plants from the same spores they grow from to ensure their survival), and they require Hive ships to eat and multiply and the time to do it in, while all Orks need to repopulate are microscopic spores and a bit of time.
 * This is true as the new material say that YES the Tyranids are a major threat, and that YES the Necrons are a serious threat, and that YES the Orks are also a serious threat, but here's a few things... the tyranids are a galaxy wide plague, but the main Hive swarms are tied up with the Orks. The Necrontyr are extremely dangerous, but they've got nearly nothing to them. Only a few dozen tomb's are active, hundreds are corrupted or destroyed, and, all in all, billions of years have taken their toll upon these killer machines. The Eldar aren't doing much, since they don't have the numbers. The Dark Eldar simply cannot afford to get into a massive war, so they are simply pirates. The Tau, on the other hand, have problems of their own, and are using resources to fight of BOTH alien invasions, and a Warp Storm. The Orks, being Orks, are heading for the biggest fights they can find, so they're just fighting everywhere. At the moment, everyone is pretty much leaving the imperial empire alone, 'cept for the latest Black Crusade, who have seen the state of the galaxy, and think it's a great time to invade. The Imperium, meanwhile, is protecting it's borders, and dealing with the 13th invasion by Failbaddon.
 * Necrons are mostly local problem - it's about holding a habitable or resource rich planet. If the body in question had zero value for the Imperium at this point, Navy can  blast it until they cannot detect anything other than half-molten gravel, and then declare quarantine over an area in which the resulting cloud of debris is discernible with a telescope, like it happened at Skopios. Tyranid swarms on surface would be little more than big juicy lance targets too, but bugs got silly amount of krakens, hive ships and whatnot to keep the Navy busy, and they disrupt astropathic communications, so the help may come too late and/or not prepared for the particular enemy.

Things are just as GRIMDARK for the Tyranids as the Imperium and Eldar
Seriously... this is a starving race running from some horrid entity (or from starvation to a new food source), and it turns out instead of a hospitable galaxy with the food to support their continued existence, it's entirely infested with nothing but the most incredibly Badass, incomprehensibly destructive, and Frighteningly Competent killers in the entire universe, all honed to martial perfection through fighting a Forever War for several millennia. The Tyranids now have to try to evolve and compete against these, consuming as much biomass as it can, and pumping out nothing but warriors or harvesters, that waste biomass and life (They can reclaim it eventually... but it's still a waste of life, and takes time) and exacerbate their hunger issue just trying to survive... Gotta eat to sate its hunger, but if it diverts the biomass to satisfying itself, it will run out of defenses against these Orks, Tau, Humans, Demons, Eldar, and Necrons, but as it continues to spend all accumulated biomass on Warriors and harvesters to keep up with the demand, it's starving itself.

One of the missing primarchs turned to Chaos, the other didn't
In the novel The First Heretic, a Heresy-era Word Bearer Marine witnesses ten primarchs landing on their homeworlds in their stasis pods. Although none are named, they are identifiable in context: Magnus psychically deconstructs his pod around him, Fulgrim crashes on a barren world and is described as "inhumanly handsome," etc. All of them, except the first one mentioned, are traitor primarchs. But the first, mystery primarch is only described is having hair "as black as the armor of the legion he would lead." This could be referring to Corax, however this wouldn't make sense as Corax was a loyalist. Either he was randomly thrown in with the nine traitors, or the black-haired primarch is one of the missing ones.
 * Black armor? Sounds like the Black Legion and Horus. Do we know Horus's hair color?
 * In at least one work of official art for the Horus Heresy, he's bald, unfortunately.
 * Also, before becoming the Black Legion, the Luna Wolves wore gray, not black.

Kroot are evolved Mudokens
Both races are descended from birds, share similar nature-based themes, have low health, low tech, and have similar hair-feathers.

Cyphers trip to revive the Emperor is a Xanatos Gambit to have the Lion and Dark Angels defect to chaos
Think about it. We know the Dark Angels only follow the codex in name, with their brother 'chapters' all being controlled by the Deathwing cult who are obsessed with capturing all the 'fallen angels' without the Imperium as a whole knowing of their 'shame'. To the point they canonically will abandon campaigns they are sworn to in order to chase the mere rumor of a Fallen angel.

How do you think they will react when the most Infamous Fallen angel Cypher saves the Emperor? It would be child's play for the Ruinous powers to twist that anger into their service. Why should Chaos settle for the crumbs of Fallen angels, when they can have the whole cake instead with a extra Primarch on top. (And what does Chaos lose by the Emperor reawakening? The Imperium is far to superstitious and fractured now for his plans on the great crusade with tons of political crap he'd have to wade through of ppl who are to used to being in power. To say nothing of the Necron and Tyranid threat approaching he'd have to focus on. )
 * addendum... it does put a rather more sinister light to the Captured Luther's ranting about how the Lion will 'forgive him'.... by apparently joining him in the thrall of chaos.

The Emperor was preparing the Imperium for the awakening of the Necrons.
We know the Emperor captured and peered into the mind of the void dragon. Before setting into motion several long Xanatos Gambits. From Mechanicum we also know from the scene where the new guardian of the Dragon was chosen this also showed some scenes of the future. Presumably the existence of the Necrons and their reawakening was also learned by the Emperor. Hence why a unified Imperium of mankind standing ready to swat the Necrons as they awake being his long term goal in order for humanity to survive.

It also might explain how the Ruinious powers blindsided him. As he'd be taking the glimpse of the future from his brief exposure to the Dragon, whom as a C'tan is blind to the warp. Thus any glimpses of the future would have no mention of the ruinious powers, leaving the Emperor to assume they wouldn't play a role in the future threats to humanity. Because he has no way of knowing the Dragon is blind to the warp.

There is 1 Chaos God above/equal to the others, the God of Fear
Simply, fear is the ultimate emotion. All of the other Chaos Gods draw from emotions that are traceable to fear, yet there seems to be no great being of pure fear in the Warp. Even though fear and the Warp are like hazelnut butter and cocoa together. To top it off, most people under the Imperium are controlled by fear of the xenos. Man itself would fuel this new god. And the other Chaos Gods may logically just be aspects of it:

"''"Fear. Fear leads to anger, leads to hate. Fear breeds terror, brings despair. Fear tries"

to multiply and fade away, it craves the presence of others, lusts for sensations that let it be forgotten for a time. Fear drives change, anything to be other than itself. It is simple, unreasoning, and the constant companion of humanity."'' "--Shinji Ikari, Shinji and Warhammer 40 K"

Not sure how it ties into the God-Emperor is a Chaos God/Malal still exists theories, but it should still hold water.
 * How does this work with Tzeentch who is the god of hope the polar opposite of fear.
 * Not really. We don't fear instead of hope, we hope in the face of fear, just as we can respond to fear with senseless violence (Khorne), mindless indulgence (Slaanesh), or apathetic acceptance (Nurgle).
 * Pity that fear is already a small portion of Nurgle's sphere of influence.

The favoured warriors of Tzeentch are... the Space Wolves
Tzeentch. The Lord of Change. Who's canonical champions are... pretty much just piles of dust sealed inside their armour so that they cannot be warped by Tzeentch's influence. Meanwhile, amongst Tzeentch's greatest foes are the Space Wolves. Werewolves. Changelings. Just. As. Planned.
 * Also, the Space Wolves main characteristic is going in, fucking up everyone's shit, and destroying even the most convoluted and impenetrable of plans by repeatedly punching it in th throat. Because against the indiscriminate forces of change, no machinations are safe. Definitely Just As Planned.

The creation of Slaanesh and the Eye of Terror, and thus, almost all of the Eldar, was caused by a game of Sburb.
I don't know where the idea came from, it just popped into the old think pan.

And besides, it's not like all the shit that this entails could possibly make the 40k-verse any WORSE.

Halo and Warhammer40000 takes place in the same universe
The anti-Xenos attitude of the IoM is racial memory left over from first, the Human-Covenant War, then later the Human-Elite War. The Primarchs were created to emulate the Master Chief in every way, including gender. After the GEoM's Spartan-II equivalents were stolen, he re-created the Spartan-IIIs, the Space Marines.

Craftworld Eldar are being set up for an eventual Guard-Type Codex Revival
Okay, this'll take a bit and it's actually a little less optimistic for the Eldar than the title indicates. First of all, the basic point is that Eldar right now can't win a break, even it seems in their own fluff. They're being beat up on all sides. Sure sounds like the Guard right before their codex jump... sort of. The Eldar are still missing two things that the Guard had before they got their codex, and this guess is mostly a prediction of how they might get them.

When I started in Third Edition, Eldar were the gorilla in the room for one reason: fast. They were above and beyond the army for fast mechanized forces, and they ran circles around everyone. It fit their fluff. Thing is, other races got into the gambit, and now the ultra-fast mechanized attack squad is as much or more a Space marine tactic, and the new Dark Eldar codex has taken over the mantle of ultra-quick, heavily armed vehicles. Eldar need something new to fit their fluff. Thing is Fifth Edition also introduced something else that the game hasn't seen in a while, really powerful Psykers. I've heard a number of complaints that Marine and Guard Psykers out-power anything in the older codexes, even in Eldar and Chaos that fluff-wise should perhaps have stronger ones. But notice that Imperium Psykers seem to lean heavily towards the “blow stuff up” end of the powers scale. Eldar Psykers could be the answer to their lack of a distinctive army style, in the form of board manipulation. Eldar Psykers could get more abilities like Eldrad's Divination, say “move target allied unit within 12” up to 2d6” in a chosen direction.” I'm keeping my idea to allies to avoid the complaints that Lash of Submission still produces, but it'd still open up an entire new set of exploits that would go a long way to making the Eldar into Difficult but Awesome, which is my impression of what they have been intended to be.

The second thing the Eldar lack is positive fan identification in the form of a tie-in story, a la the Ciaphas Cain and Gaunt's Ghosts novels. I don't think Pirates of the Caribbean: Yriel Edition is a good idea, but it still remains that the one major fan-followed Eldar character is Eldrad Ulthran, and he's looking pretty dead. I think this could actually be the start of the story the Eldar need. Have a young prophet rise up, say Q'sandria the student from the codex, saying that Eldrad's presence in the Warp is in order to jumpstart the rise of Ynnead and go on a long campaign to unite the craftworlds in harvesting souls to feed the birth of the new God, and you've got the makings of a novel series that has the kind of creepy, disquieting but powerful premise that fits the Eldar fluff but can still be compelling to readers, watching the race unite under the banner of what amounts to a carefully organized mass suicide while the forces around them try to thwart their fragile, careful plans. Each of the craftworlds can join for their own reasons and bring their own methods and issues, for example Iyanden offering the wealth of it's Infinity Circuit but requiring that the God incubate for some time in the Craftworld to honor the lost, or Saim-Hann wanting to feed the God the souls of “lesser” races and thus clashing with the more doctrinaire Ulthwe Seers. The Picture of the Eldar moves away from The Dying Race to a more interesting and compelling patchwork of survivalists uniting under their new hope, created in the same way as their greatest foe.

Obviously, this'll take a while to do, but it'd be an interesting result of the army's current decline. I can even think of how this could potentially screw with things and make the setting worse, if Ynnead wakes up and decides that it isn't satisfied with the Eldar souls it's been fed, and maybe its corrupted with other souls in it as well. Suddenly the Deceiver isn't the only C'Tan with an Eldar God counterpart wandering around. And besides, the Eldar as a united force with renewed hope for reestablishing galactic dominance is not something the Imperium really wants to consider right now.

The Power of Love could easily turn the tides of the battle by weakening The Chaos Gods
Sounds really stupid at first given how dark the setting is, but taking account that The Immaterium is the collective psyche of all sentinent beings in the galaxy, if a considerable amount of defectors drom decadence formed another faction made from their alliance with each other, if they changed their way of life to a more peaceful, caring and stable one and just resorted to violence when defending themmselves from other factions, the gods and daemons from The Warp would either take a severe blow in their strenghts or start transforming into more benevolent entities, specially Khorne who relies on violence and war to keep powerful, and Nurgle, who is the god of despair and decay. This shift in the balance of power would make things a lot easier for the other factions, now being able to concentrate on the Tyranids, the Necrons and the Orks. Seeing that following the Defectors ais a good idea, more and more people would migrate to Defector's territory to improve their way of life, which further weakens the Chaos.

Of course, all of this is easier said than done given how convulted and confilctive this verse is.
 * Pity theres a chaos god of love, aka Slannesh. A really evil, perverse god of love but still.
 * I think Nurgle, the "friendly" god of diseases, is the god of Power of Love you were talking about. Slaanesh is more like god of lust.

M'kran's identity.
Tzeentch has a prince on level with Doombreed named M'kran. Given that Doombreed is likely Genghis Khan, it's possible that M'kran is actually Pericles.

Have we truly missed this one? Hope. Change. ''Hope. Change. M'kran is obviously'' Barack Obama.

The Dark Eldar are about to get royally screwed by Tzeentch
At first sight, true to the crapsackiness of the setting, they're the only kind of Eldar to have prospered since the Fall. And as usual, their new codex shows them as being extremely dangerous and a real threat to the rest of the galaxy. However, once you start to read the special characters bios, you start to notice that things are starting to get messy for them. Kheradruakh, the most powerful mandrake, is actively working at the coming of the powers that turned the mandrakes into what they are - that is, heavily mutated Eldar with magic powers. Urien Rakarth's regeneration is less and less reliable and turns him, once again, into some kind of mutant ; maybe indicating that the Dark Eldar will soon start to think twice before using their regenerative technology. Lady Malis is actually possessed by something that allows her to predict all of her opponent's moves and to plot her next attacks accordingly. And Asdrubael Vect's grip on Commoragh is starting to slip, maybe as some kind of Xanatos Gambit against his enemies, but nothing's telling us that he'll manage to regain complete control if that's the case. Mutations, magic, ability of seeing the future and manipulating events, and possibly a master plan going into shreds at the last minute... Yep, looks like the kind of tricks Tzeentch routinely pulls out. They've survived the birth of the Chaos God they've created, only to fall thanks to another one.
 * Except the Mandrakes aren't so much mutants as hybrids of Eldar with some sort of shadow creature from a dimension that isn't the Warp - in fact, there's a lot of hints that there are non-Warp dimensions out there, and that is what the Decapitator is serving. The entity that Malys confronted in the Webway laughed, implying she's more of a pawn of the Laughing God now. And Urien Rakarth is only going crazier and semi-mummified by the ressurection cycle, not actually mutated.

The Eaters from Chimera Beast are the Tyranids
A bit of a given considering how they are a Horde of Alien Locusts who acquire powers through eating other beings. This makes the "Bad Ending"  at least semi-canonical, albiet, with   being replaced with.

The Angry Marines are descendents of the Imperial Fists.
I know, I know, a Wild Mass Guessing about a homebrew chapter... Anyway... The first clue is their colour scheme, but when we take a look at the Imperial Fists' history, we can find some other things that tend to relate those two chapters. The Imperial fists are known for being among the most ruthless chapters of the Imperium, and as being particularly violent. They're the ones who held the last lines of defense during the siege of Terra, and boy, did they give the traitors a hard time... The chapters created from them tend to display similar levels of toughness : the Crimson Fists, instead of trying to recover from the destruction of their chapterworld, continue to fight with all they've got in one last, extended blaze of glory ; while the Black templars started a millenia-long crusade against everything that threatens the Imperium, picking up fights wherever is necessary and without any restraints, without having necessarily been asked to intervene. Another element is that after the Horus Heresy, the Imperial Fists were vehemently opposed to Guilliman's Codex Astartes, to the point of almost starting another civil war, before they'd reluctantly agree to follow its principles on certain conditions (and the Black Templars even publicly show they don't give a damn about the Codex Astartes). Even though it's treated as comedy and as a way of showing to Games Workshop what 4chan thinks of the Ultramarines, the Angry Marines have frequently flipped the bird to the Ultramarines and the Codex Astartes. So, either they've been created from the most unstable elements of the Imperial Fists, or they've split up because they were disgusted that their brethen would give in to the Ultramarines' demands.

Chaos will ultimately be defeated by a power older than even the C'tan
But not one which actually hates them, as they can not truely hate, but only get annoyed at the mess that they make. They see the Chaos Gods as being the sum of everything they disaprove of, sloppy crude thinking that gets in the way of the efficient running of the universe, simply piling up the paperwork. Ultimately when chaos ends, the last moments of the chaos gods shall be witnessed by trillions opon trillions of identical grey empty robes floating which will tell the fading beings this... "To be an individual is to Live, and to Live is to Die"]

The Blood Ravens' Unknown Primarch is/was one of the missing two Primarchs
Nobody knows about the Blood Ravens' origins, not even the Ravens themselves. So it's a possibility that one of the 2 chapters deleted from Imperial records and their Primarchs is in fact the founding Primarch of the Blood Ravens.
 * I've heard theories painting them as loyalist Thousand Sons, which would explain the hoarding of information. Certain higher ups do know this, but telling the rest of the chapter is just asking for trouble.
 * Hoarding of information, plus their high proportion of Librarians and the fact that they combine the office of Chapter Master and Chief Librarian...

Varro Tigurius is a sensei
Tigurius can interface with the Hive Mind, a feat previously thought possible only for a psyker as powerful as the Emperor.

The sensei theory states that, prior to ascending the Golden Throne, the Emperor has children who inherited His psychic powers.

Since Tigurius is evidently nearly as powerful as the Emperor, it's possible he is descended from Him.
 * Aren't Sensei all Blanks?

The past identities of the Emperor
Include Charlemagne and Julius Caesar.
 * And Jesus, Buddha, and the greatest pre-Imperial statesman humanity has ever known: Theodore Roosevelt.

Revolution of the Imperium
The Emperor, upon dying on the Golden Throne, will come back to life. He will be invigorated, as his soul was bolstered by ten millennia of worship. This is the least important part.

Having recognized that the Chaos Gods are weakened by being replaced, he will no longer disallow worship of himself. In fact, the Emperor will accept and subtly encourage his image as a deity. He will, however, face great pains with reforming the Imperium to be not so brutal and dystopian.

Primarchs will also return as their father is resurrected. Not just the loyalists, but traitors as well. Here's how it's gonna go down:

Lion el'Jonson and Roboute Guilliman will revive, mostly because they have sensed their father's soul awakening. Vulkan, Russ, Corax, and the Khan all return as well, knowing that they have critical tasks ahead of them: the Imperium must be reforged as it was during the Great Crusade.

Alpharius/Omegon, realizing that the galactic stage has changed so much that their gambit no longer matters, will return to Terra, bringing the Alpha Legion with them.

Here's where it gets interesting. A few actual traitor primarchs (Alpharius doesn't count, for reasons that are obvious if you've read Legion) will attempt to return to the side of good, and each will be given a herculean task to complete. Fulgrim's possessing daemon is destroyed by the psychic shock of the Emperor's return. His body slowly returning to its former perfection, Fulgrim fights his way out of the Eye of Terror, begging forgiveness from the Emperor. He is absolved. A few renegade chapters, now returning to the fold of the Imperium, are handed over to Fulgrim's command until the Emperor's Children can be rebuilt as a legion proper. Fulgrim's task: recruit the Eldar and Tau as allies in a war against the Chaos/Necron/Tyranid threat.

Magnus attempts to parlay with the Emperor, after all he originally supported his father during the Heresy. The Emperor, furious with Magnus's disobedience to the Council of Nikea ten thousand years earlier, sends Magnus on a Crusade into the Warp itself to outsmart and destroy the Chaos gods. Supporting him are the Black Templars and Grey Knights.

Finally, Lorgar. Now aware of his Father's presence in the warp, he is almost blinded. The constant psychic bombardment of the Emperor's light is torture, a reminder of the perfection of good, so opposed to the corrupt Chaos gods. Lorgar manages to bring some of his Astartes with him, begging the Emperor for forgiveness much like his brother Fulgrim. Again, he is forgiven. He is sent to parlay and convert the remaining traitor primarchs: Angron, Mortarion, and Perturabo.

Snotlings are the descendants of the Old Ones
Modern Ork oral histories describe both the Old Ones and the Snotlings as their creators. Why can't both be true? Perhaps, after creating the Orkz, a small number of Old Ones managed to survive all the crazy shit that was going on. Over time, their Ork servants gained more and more power over them, causing the surviving Old Ones to degenerate into Snotlings.

This would mean that the Old Ones were also a sentient fungus, so they evidently based the Orkz on their own physiology.

Gork and Mork both embody cunning brutality and brutal cunning
We know that chaos gods are shaped by the beliefs and actions of their followers. Since the Orkz can't agree on which of their gods is which, who is to say that the gods themselves stay the same? Most likely, Gork and Mork constantly switch between being cunningly brutal and brutally cunning, and thus giving the Orkz something to fight over.

Matt Ward hates his job.
And is trying his hardest to get fired the only way he can, by making codexes that leave the fans howling in incoherent rage.
 * That, or Mr. Ward had sat down and said to himself "Screw the Rules, I Make Them!"

Kharn is actually quite intelligent outside of combat.
Think about it. The fluff says that he's the voice of reason during Angron's temper tantrums. Yet the rules list him as an ultra-violent death machine. How can he be both? Well when he's not in combat, he simply bottles up his anger and acts in a very calm and collected manner. Then, when he gets out on the battlefield, he lets out all his repressed anger, making him even more destructive than any other World Eater.
 * Actually, that would explain how he still manages to be a pretty fun guy when not collecting skulls for the skull throne.
 * Kharn has appeared in novels before the World Eaters turned traitor. He was a pretty standard honorable warrior type that went insane when the legion turned traitor. His "Betrayer" status most likely comes from him sharing more in common with the loyalists, but not ever realizing that was an option before it was too late.
 * Kharn is called the Betrayer because he slaughtered his own legion along with the majority of the Emperor's Children on Skalathrax because his fellows betrayed the ideals of Khorne's Faith by seeking shelter from the lethal cold instead of getting into the thick of it and killing the enemy.

The reason Guardmen's weapons and armor are so crappy
The Administratum knows that once an ordinary man turns to Chaos, he won't come back. So in response, they make sure they're as easy to kill as possible.
 * Nope, its explicitly stated that the reason is because human life is a cheap resource in the Imperium. The Imperial Guard wins battles through attrition. There is no point giving high quality equipment to someone that is basically being used for cannon fodder.

Every time the Inquisition orders an Exterminatus, Chaos just gets more powerful.
From Kyras' speech at the end of Retribution: ""In mere hours, billions will die! Innocent! Guilty! Strong and weak! Honest and deceitful! ALL of them! They will scream, they will burn, and for no purpose but that mighty Khorne may revel in their bloodshed!"

Who's to say that this particular Exterminatus is special?
 * I remember reading somewhere that Virus Bombs, a certain type of Exterminatus involving a hyper-contagious flesh dissolving disease, aren't really used anymore because Nurgle gets power from an entire planet being infected.

Warhammer 40K is set on the future of the universe of Starcraft.
The Emperor is Arcuturus Mengsk, a descendant of Mengsk, or whoever is in the charge of Terran Dominion. That guy had augmented himself to the point of becoming a Physical God. Yeah, the Terran Dominion has become the Imperium of Man. Moreover, as Zergs predicted, the psychic potential of Terrans has expanded, making them a powerful psionic race. Eldars are offshoots of Terrans with gigantic psychic potentials, but their horrific mutation also takes toll to their ability to reproduce and endurance. Protoss have now become Necrons, becoming the Protoss/Zerg hybrid (Necrons have regenerative powers, mind you, and so do Zergs, I guess?) and losing their soul and Psychic Powers in the process. Xel'naga are C'tans or the Old Ones, or maybe both. Other races were not discovered at the time the events of Starcraft happened.

The origins of the Adeptus Mechanicus is in the Dark Age of Technology
From the Lexicanum ''The Age of Technology is thus considered "dark" in the Imperium's current age. It is also considered a dark age because mankind in the Age of Technology had come to worship science as God.'' (emphasis mine) What is the basic tenent of the Cult Mechanicus? Knowledge is the supreme manifestation of divinity. It's possible that the Cult Mechanicus grew out of the distant and half-formed memories of the science-religion of the DAOT, keeping the basic ideas alive in a way that would be completely alien to the residents of the Golden Age of Mankind.
 * Isn't this canon already?

There are no aliens or Chaos gods.
The Imperium is an Orwellian space empire that simply makes up various threats in order to justify increasingly totalitarian rule. The Emperor is a fictional Big Brother figure - the Great Crusade and Horus Heresy never happened. Occasionally the Imperium blows up a planet or stages a fake alien invasion for PR purposes. The Space Marines are just juiced-up psychopaths sent in to brutally supress uprisings against the government. Perhaps Chaos serves as 40k's equivalent of the Brotherhood - occasionally Inquisitors will pretend to be agents of Chaos to entrap potential dissidents.


 * Or maybe the aliens do exist, but were all genetically engineered by humanity pre-Dark Age of Technology in order to justify having such a strong government, along with the "daemons"?

The Primarchs will return.
With the Imperium reaching what is considered the end of existence as we know it, the Emperor, in his semi-aware state in the Warp, will send out the dead Primarchs (Sanguinius, Rogal Dorn, and Ferrus Manus) back into the regular galaxy. He will also send mental summons to his still living loyalist Primarchs (Leman Russ, Corax, Vulkan, Jaghatai Khan) who have promised to return for the final battle, to gather in a world in the Eye of Terror. There, they will use lost technology to heal Roboute Gulliman and Lion'El Johnson of their wounds. With the Adeptus Terra having spent literal millennia indoctrinating the average Imperial citizen to honor the Primarchs as martyrs, the people will rally to them. Further bolstered by their Legions, Gulliman will resume his position as Lord Commander of the Imperium and serve as the Primarchs representative among the High Lords of Terra, and become the leading voice among the Council. Not pleased with how the High Lords have mismanaged the people of the Imperium, Gulliman will begin "advising" them on how to make the lives of the people of the Imperium better. The Primarchs military intellect will help turn the tides against the Tyrannids, the Necrons, and Chaos Undivided, and give the Imperium some breathing room. This will not be without problems, however. The Administratum will be unaccustomed to having someone more powerful than them, the Ecclesiarchy will be unaccustomed to people who can legitimately claim to know the Emperor's will better than them, and the Inquisition will be unaccustomed to someone who can order them around.

The antagonist factions will all be given a lighter shade of gray
based on onfo from the upcoming Black Crusade RPG that gives a sympathetic view on Chaos itself, futer editions of the game will do the same for the Tyranid, the Necrons and even the Dark Eldar, they'll still be evil obviosly, and it's still going to be a crapsack universe but this will effectivly kill darkness induced audience apathy.
 * The Tyranids, Necrons, And Dark Eldar really have no room for good.
 * The Tyranids are a Hive Mind and the entire species is effectively one being.
 * Arguably, the Tyranids are doing what they do out of hunger; could they really be seen as hated any more than a lion can be hated for eating a gazelle?
 * Yes but lions and gazelle aren't sentient humans and the hive mind are and yet the hive mind still goes after human planets rather than just eating all of the death worlds and planets with no people on them that arguably provide more food.
 * The Necrons are either two insane or so close to brainless that they have no real hope of being good.
 * The Dark Eldar codex used to open with the line "This is a tale of evil incarnate" that stance has not changed over time.
 * They do seem to do what they do in order to survive; perhaps given the proper alternative, they might stop their current course of action?
 * Chaos has always had a lighter side, people like Magnus The Red who join chaos out of desperation or simply misguided fools who believed they could save people with the power of Chaos the problem being that Chaos corrupts entirely turning paragons of righteousnesses into bloodthirsty berserkers and the light.

One of the missing primarchs was a pariah
It makes sense in that every primarch has his own "hat," as it were. Psychological warfare primarch? Check. Humanitarian primarch? Check. Unconventional warfare primarch? Check. There isn't, however a pariah. It also makes sense that this primarch would be ejected from the Imperium's memory. The general hate most people develop towards pariahs might almost be enough, but then the fridge horror sets in: because Astartes tend to take on the qualities of their primarch, aspirants of this particular missing legion lose their souls. Knowing the 40k universe, the process would be particularly unpleasant.
 * What's more horrifying is that since he is a Primarch he probably wouldn't have just been a regular Pariah, but an immensely powerful pariah. Considering that a modified human pariah (Spear) was capable of killing the emperor, imagine what a Primarch level Pariah could do. Hell the emperor probably couldn't even pick him up in person like he did when he found the rest of the Primarchs.
 * Pariahs can be overwhelmed by too powerful Warp entities, too. But either way there probably were no hugs.
 * Then he is likely to have something to do with the Sisters of Silence. And/or the Emperor, knowing well what his main enemies are, kept this "secret weapon" out of limelight. Unfortunately, he had to teleport onto a ship for the final showdown, so the biggest ace up the sleeve was left behind and not used - bad luck or Chaos trickery?

One of the missing primarchs is Duke Nukem
Time travel has been established as being possible (orks killing themselves in the past to get their favorite gun twice and whatnot), so it is entirely possible that the two missing primarchs ended up lost in time, rather than just in space like the other 18. Perhaps one went to the past, and ended up being the most absurd insane super human in the history of the universe, Duke Nukem. While he might not quite have the same height as some of the other primarchs (who were much taller than normal humans; estimates seem to run from around 2-3 meters), he certainly has their strength, toughness, and skills.
 * His legion would naturally be called the Steel Balls.

Tzeentch has David Xanatos, Light Yagami, and Lelouch vi Britannia as his three most elite and powerful Daemon Princes.
Of course, they all jockey for the top position (Xanatos would naturally fancy himself as Tzeentch's "Number One"), which not only involves their own schemes but also the sabotage of their rivals' plans. All of this, naturally, is according to Tzeentch's keikaku.

The Chaos Gods were incarnated in the image of their respective race's concept of ultimate evil.
Slaanesh seems to be a corruption of the Eldar, whereas Khorne (said to be created by humans) and his daemons appear to be more diabolic in appearance. As to Nurgle and Tzeentch, who can say?
 * I would say that Khorne would be the ultimate evil for the peaceful (or at least peace-seeking) Tau, Tzeentch the Lord of Change would be the greatest evil for the imperium (who has been worshipping a former hero for 10000 years), nurgle would be the orks, as disease is the least orky way to die, and slaneesh would be eldar, as previously stated.
 * It was expressly written out in one of the previous codexes that Tzeentch, Khorne and Nurgle were all spawned by humans. This is because, unlike the Eldar and other psyker races that were created to be Psykers by the Old Ones, humanity just kind of accidentally stumbled onto it through evolution. There was no plot, no training, and while only a scantly small percentage have any sort of psychic ability, every human has a psychic signature. It was all this untrained, unknowing turbulence that most recently stirred up the Warp, and why the Chaos Gods were far more vague and dark than those that came before (namely, the C'Tan and the Eldar gods). Mankind, as a species, has always accentuated the negative, and most of our progress until very recently has been based off of "How can we avoid the bad?" rather than "How can we enhance the good?" THAT said, the reason Slaanesh was spawned from the Eldar is because, as nearly an entire race, they turned to abject hedonism to the point that the streets of their homeworlds ran with the blood of pointless sacrifices and mindless infighting while the others laughed and did drugs and sang ate and fucked and stabbed each other good-naturedly, and such strong psychic turbulence over such a short (in cosmic terms) time led to not just the birth of a new Chaos God, but a birth that ripped the physical dimension a new asshole, that we now call the Eye of Terror.

Tyranids are Warp-touched insects.
Given their ravenousness, their ability to interfere with the Warp, and their destructive nature, who's to say that they're not merely affected by the Warp? We already know that there are insects in the Warp, and they multiply by feeding on people's innards, so perhaps the Tyranids are tied to them.

Warhammer 40000 exists in the Fallout timeline.

 * The Blood Ravens seem to be obsessed with collecting tech, like the Brotherhood of Steel.
 * Green-skinned homicidal maniacs--Super Mutants or Orks?
 * The Forced Evolutionary Virus could be a Warp-based mutagenic virus--look at what it did to everything from Deathclaws to Centaurs.
 * The status quo in the 41st Millennium remains constant, a war without end. And war... war never changes.

The Emperor was a Professor Guinea Pig.
So, the big man has been around for almost as long as human civilisation, taking a variety of different identities, usually as a soldier or an advisor to the powerful. Funny thing is, there aren't any legends of, say, a ten-foot-tall Roman centurion with a shiny head; he was able to pass as a normal human. He could have messed with people's perceptions, but the far simpler answer is that he hadn't always looked like that. Also remember that he was a bioengineering expert, and that the superhuman abilities the Primarchs inherited from him could be refined into a set of specific implants to make Space Marines. It seems to follow that at some point he experimented on his own body to strengthen and perfect it, using psychic biomancy instead of anything as crude as surgery or retroviruses. He was literally the testbed and prototype for the Primarchs and Astartes.

A Stick COULD Fire Bullets If An Ork Thought it Could, Depending on the Ork.
Imagine seeing an ork in a forest in a forest on your homeworld. You stay quiet, so it doesn't notice you. It does, however, notice a stick that it thinks looks kind of like a shoota. The ork experimentally pulls a twig that looks like the trigger, and a bullet comes out and hits it in its foot. Limping, the ork leaves. Congratulations, you have survived encountering an ork psyker, albeit one that failed its shoota safety course. The theory is basically that an ork psyker can make anything do anything a non-ork pysker could do, thereby allowing an underinformed observer to think thaat all orks can make anything do anything. This nicely helps explain why some sources explain that orks can use sticks to fire bullets and others claim that ork technology only works better because of the ork psychic gesalt thingy. Of course, almost everything this troper knows about Warhmmer 40k is what I know from reading this wiki, so I might be saying stuff that makes no sense to anyone who has more knowledge.
 * Eh... the whole "orks could make a stick shoot bullets" is just an fan exageration of the fact orks make things work in certain ways because they think it should. A stick could NEVER shoot bullets by itself, but a badly made gun COULD be made to shoot better then it should.
 * The idea is that if an ork was about a powerful enough psyker, he could unconciously use his psyker abilities to do what his orkish ones can't. Also, having learned most of what I have about 40k from this wiki or that of 40k, I was under the impression that the "stick fires bullets" was partially supported by some source or another.
 * Absolutely impossible, there is no such thing as Shoota Safety Skool (Safety takes all the fun out'a da shootin!).

Chaos and humanity will win.
As the tyranids, orks, and necrons drive humanity to the brink of extinction, the Emperor will finally step off the throne... and immediately forge an alliance with Chaos. Humanity and daemonkind will merge. One by one, Imperial worlds will become daemon worlds. And the universe will fall before the infite power of Humanity Undivided.

Things are about to get better...
So far as I know, the only ways the 40k universe could get worse would require either the destruction of one of the main races (reducing model sales and alienating fans who like he race and/or think it would survive that, also hurting sales) or that of the galaxy/universe (which would also impact sales). Being a company, Games Workshop will not do stuff that will adversely affect sales when there is another option. The Dark Eldar are fading. The orks decide to wage a WAAAGH!! (did I spell that right?) against the tyranids and/or the necrons, ridding the galaxy of one or two of its major threats and tying up another. The Emperor awakes and sets humanity on a brighter course before making a pact with the Eldar and the Tau against Chaos. And then, as fans scratch their heads, the end of the main rulebook hints at a greater danger, one which ceases the orks' WAAAGH!! and recruits the dark eldar. It gets much, much worse as time goes on. This allows new figures (the new faction, maybe eldar/tau/etc Imperial Guard or even space marines) and would be unexpected for a game whose world has gotten steadily worse with each edition, and another when it fails to be good in the end. It makes sense, at least.

The creation of Slaanesh and the Eye of Terror wasn't just the sole responsibility of the Eldar. Humanity during the Dark Age of Technology also had a hand in it
It's implied that humans have been able to create three Chaos Gods, so why would Slaanesh be a sole exception, considering that humanity is also kinda hedonistic (/b/. Enough said). It's also implied that during the Dark Age humanity has come to regard science as God and grow arrogant, just like the eldar. I can actually see it that in this scientism and arrogance humanity started losing moral standards (well there is no scientific proof that Sex Is Evil, right?) and eventually became an extremely hedonistic Bread and Circuses society, ala Brave New World, and sure humans aren't as psychically powerful as the eldar, but they make up for sheer numbers. Also, this would pretty much fit in with the "Humanity = Rome" to the "Warhammer 40k = Dark Age Europe in space", considering how it wasn't just outside Barbarians that brought down Rome, but also the incompetence and hedonism of its higher authorities.

Nurgle deliberately lets Isha whisper cures to mortals
Considering how Isha's always in Nurgle's custody, it's unlikely that he doesn't notice a single whisper. It could be that he does notice but doesn't do anything about it. As to why Nurgle would do this, there are two possible reasons: Either he loves her too much to punish her for it, or he's actually observing how the cures would defeat his diseases and then improve his 'craft' by studying better ways to make a disease more persistent. Or maybe both.

The God Emporer of mankind is The Kurgan after winning the prize
Besides the fact that they are both depicted as very large men with flowing black hair, a variety of similarities are present

1. Ramirez says, about the Kurgan "If he wins the Prize, mortal man would suffer an eternity of darkness.", and humanity in 40k is in a fairly dark age.

2. When Connor wins the prize, he says "I feel everything! I know... I know everything! I am everything!" Sounds to me like he is describing himself, and by extension anyone who won the prize, as The most powerfdul psychic of all mankind.

3. The God Emporer of Mankind was said to be born in the second millenium B.C., or usually some time around the dawn of civilization, which, given the Future Imperfect history in 40k, is a fairly acurate estimate.( The Kurgan was born in 970 Bc)

That being said, I could easily imagine The Kurgan having more than 20 sons in his life(though i would not see him letting many more than that live), he would most likely be frightened by the realization that he is no longer immortal, but it turned out alright, because The Emporer is, for all intents and purposes,unable to die.

Lorgar was abused as a child by Kor Phaeron
Firstly, Kor always calls him dismissively "boy". Secondly, during the scene in The First Heretic --this does not seem like the behaviour of a loving parent...

Chaos is Four Chan.
Isn't it pretty obvious? First, the number of Chaos Gods. Four. 4. Chan. Second, the concept of daemons. Thoughts and beliefs turning alive... like, sentient memes? Third, the Warp is basically the Id of the entire universe, a chaotic realm with no rules and laws while dominated by various memes. Again. Like 4chan, the Id of the Internet. And the fourth and the most important. Chaos Gods themselves. Khorne represents the rage and hate-machinery of the Anonymous, Slaanesh represents the Rule 34 and the idea of The Internet Is for Porn, Tzeentch represents Anonymous' surprising intelligence and Magnificent Bastardry which they can show sometimes (especially in acts of trolling or rebellion, after all they were inspired by V for Vendetta), and Nurgle represents Anonymous' decayed standards and the disease-like nature of memes in general (well Richard Dawkins coined the term meme as the cultural analogue for genes/virus).

China took over the world and became the Imperium.
China took over the world and conquered planets and star systems, only to fall apart to pieces. One day, an obscenely powerful psychic was born, reunified the galactic empire, and became the Emperor. The rest is history.

The Emperor wakes up... and destroys the Imperium of Man along with the rest of the universe.
The Emperor is back from the near-death either as the Star Child or via the sacrifice of a Sensei. Sadly, instead of rebuilding Imperium, the Emperor becomes a Chaos God even more powerful than Nurgle, Tzeentch, Khorne, and Slaanesh combined... Sick and tired of being locked up inside the Golden Throne and watching the galaxy burn, the Emperor proceeds to destroy the very fabric of spacetime, harvesting human souls, wiping out all xenos races, absorbing and cleansing the Warp, while singing unfittingly cheerful songs. And then the Emperor will float in the empty and devastated universe merged with the Warp for the rest of the eternity, alone and mourning.
 * Alternatively, after he destroys the 40k universe, he wishes that the Warp had never existed. Cue the real world happening. Unfortunately, due to some bug in the fabric of spacetime or something, a select few were able to remember the details of the past universe, although in a deformed way.

The orks are the only sane race in the Galaxy.
In the grimdark grimdark of the future they are the only ones who seem to be having fun.

The Earth in the Neon Genesis Evangelion universe is actually an Emperor-forgotten world cut off from the Imperium eons ago.
And then an Inquisitor discovers the devastated world and orders Exterminatus, having found signs of yet another nightmare monsters that are 19th and more Angels. And then the said nightmare monsters wake up and eat the star fleets sent to the planet. And invade other planets as well. Cue the White Crusade (named for the body color of those monsters).

Alternatively, the Instrumentalized humans from Neon Genesis Evangelion evolve into the Warp, and Shinji, with his newfound god-like powers, becomes the God-emperor of Mankind
No, not Shinji and Warhammer 40 K: instead, after the Third Impact, Shinji, having retained his End of the World Special powers and thus able to draw powers from Instrumentality / Warp, became an immortal powerful psyker, and being the only surviving man, decides he can finally strip off his Butt Monkey tendencies and unify humanity (his descendants) as more of a Ubermensch this time, molding human history for millenia and finally leading to the creation of the Imperium of Man. This of course would also make a good Freudian Excuse for the Imperium's actions. Alternatively, both Shinji And Warhammer 40k and Warhammer 40000 canon are Alternate Universes Shinji created during Instrumentality with him placing himself into the role of the possible God-Emperor.

The Emperor is Sailor Cosmos with her mind taken over first by Sailor Venus and then by Sailor Galaxia, and the Old Ones were the Silver Millennium
Based on the Sailor Moon manga. The Old Ones were the humans of the Silver Millennium, noted for their incredibly long lifespan, but after their capital was destroyed by an early Chaos God, Queen Metallia, they were weakened and divided, and, after defeating the C'tan Galaxia wiped out the Enslaver Plague... And all the surviving Silver Millennium humans, leaving only the descendant of the Earth ones, with the Orks brought to the brink of extermination by her rampage and the Eldar filling the power vacuum and forgetting who created them.

Chibiusa's reign would be the Dark Age of Technology, with the dead Sailor Senshi resurrecting and Sailor Pluto and Galaxia using the late's Queen Serenity's corpse fused with the Starseeds of many historical figures as the basis for Sailor Cosmos in preparation for the emerging of Sailor Chaos.

Then the decaying Eldars created Slaneesh, and that also brought the emerging of Sailor Chaos as the avatar of Chaos Undivided and the destruction of Chibiusa's Empire, while the Sailor Senshi suicided themselves into creating Sailor Cosmos, who, after her time travel, destroys Sailor Chaos (Oh Crap ensues for the Chaos Gods). In doing so, the original personality based on Sailor Moon goes catathonic, and Sailor Venus, who became more serious after being killed by Galaxia, takes over and decides to do things her way. A more violent way. To get the time to do so, Cosmos awakens the Void Dragon and fakes her death in beating it into submission (the Void Dragon knows, but shuts up out of fear), and then, as the very scared Void Dragon inspires the Adeptus Mechanicus on Mars (chosen to honor Sailor Mars), takes a male form to continue The Masquerade and reunifies Earth while preparing the conquest of the galaxy.

The scattering of the Primarchs happens when the Chaos Gods realizes they have been had, and the Heresy is their last ditch attempt at defeating the now more violent, scheming and combative version of Sailor Cosmos, an attempt that went even too well: the Emperor allowed Horus to wound him to become even more powerful due the adoration of the Empire's citizens, and the defects of the Golden Throne are just the God Emperor stirring before awakening, resurrecting as loyal all the Primarchs and cleansing the Chaos Space Marines, before Venus' personality retires and lets Galaxia take over as she has more knowledge of Chaos of anyone. Or worse, in the last ten thousands years the personalities of Sailor Moon, Sailor Venus and Sailor Galaxia merged, giving the Emperor Sailor Moon's immense willpower, Sailor Venus' Plucky Girl, scheming and violent tendencies and Galaxia's ulterior violent tendencies, intimate knowledge of Chaos and desire to get even for that backstabbing during her battle with Sailor Moon.
 * Not even Khorne wants to face THAT...

The Emperor is serving as a Wetware CPU supercomputer for the Imperium.
Turns out the Emperor is more than a corpse. He functions as the Astronomican's software (he guides it, remember) and is making calculations and decisions for the High Lords of Terra/whatever decision makers Imperium has.

Nurgle is actually a 1984-style dictator god who pretends to be nice.
Nurgle's nice and friendly demeanor is all a lie. In reality, his worshippers are controlled like puppets by him, wearing the horrible grin of the damned and their mind and soul ground to dust by the endless prodding of a master of Faux Affably Evil. He captures potential prisoners, destroys the last good things left to their lives, and dominates them through Stockholm Syndrome, Mind Control, torture chambers, and brainwashing. Indeed, Nurgle is in fact the only Chaos God who is actively enjoying evil for the sake of it. (Khorne just wants to shed some blood, Slaanesh only cares for pleasure, and Tzeentch causes change for the sake of it...)

Nurgle is going to win and turn every single soul into broken slaves.
Second Law of Thermodynamics and sheer amount of despair will bring victory to Nurgle. There, Nurgle will eat every soul, break them into slavery, turn them into pale, shaded excrement of their former selves, and attach their decapitated and beheaded torsos (or spiritual equivalent of it) to neurons so that his realm would be powered by their sheer misery and despair. It's such a horrific fate that even Slaanesh's tortures are orgasmically pleasurable in comparison.
 * It is a fate so horrific that it tears a hole into the space, time, and even the Warp itself. Thus the world is divided by zero and ends.

Nurgle is actually a Big Good and/or a Well-Intentioned Extremist who seeks to save humanity.
A friend to all living things, Nurgle wants creatures to live happily ever after in his filthy, unclean paradise. The problem is, everyone loathes his methods of bringing happiness to the world, namely plagues, diseases, and Body Horror.

Related to the above Nurgle-the-good-guy theory, Nurgle's true form is mind-blowingly beautiful and full of light.
So beautiful, Slaanesh is nothing against him. Nurgle appears to be putrid and disgusting only because the mortals are so afraid of dying and decay. His followers, however, can see his true form.
 * So it's like Saya no Uta?

Our future will be like Warhammer 40000
We all know that in the Middle East, there is only war, and if you try to defy it, you are going to be raped by daemons for eternity for helping others. Soon, financial crisis and environmental problems will end the human civilization and take all of us to the afterlife that is WH40k. AHAHAHAHAHAHAHA
 * Imperium of Man: The vast majority who lives under the boot of an inefficient bureaucracy/dictatorship
 * The Eldar: those lucky, virtuous few individuals smart enough to do some (futile) contribution to the world
 * Dark Eldar: Corrupt Corporate Executives and other wealthy but depraved assholes
 * Chaos and the Daemons: our technology turning against us
 * That's Necrons.

The Missing Primarchs did something extremely embarassing and were grounded until the Horus Heresy, and later became Chapter Masters of an Ultramarines successor chapter
The Traitor Legions are still known to exist if you have high enough clearance, but the any record on the Missing Primarchs and their legions was expunged. Whatever they did, it was worse than falling to Chaos. This Troper has his money on one of them being Rubinek of the Iron Hearts (described as a Primarch when mentioned in a short story) and discovering the existance of Necoho the Doubter and preaching his creed to the Adeptus Custodes due its resemblance with the Imperial Truth, and the other having the power of invisibility and him and his Marines being caught at peeping. In both cases the Primarchs were grounded and their records expunged for imbecility and perversion, with their numbers being absorbed by the Ultramarines (in the case of the peepers only in part, as the Space Wolves would have killed some of them in order to bring their Primarch to the Emperor. After all, in Prospero Burns Leman Russ mentioned that attacking Prospero at the start of the Heresy was not the first time the Space Wolves fought other Space Marines). Then the Heresy came, and the Emperor allowed the Grounded Primarchs out of their rooms to fight in the Siege of Terra. Their valor was such that the Emperor declared them redeemed and annulled their grounding, but before their Legions could be reintegrated the Emperor was entombed on the Golden Throne, and Roboute Gulliman gave them their Marines back in the Second Founding in the form of two (or more) Space Marines Successor Chapters.

The ballad of John Henry, of railroad spike fame becomes, a story of an ancient heretek for the Adeptus Mechanicus.
In the story John Henry beats a steam powered hammering machine, saves his friends jobs, and dies in the end of exhaustion. In the Grimdark 40K universe this retelling involves John Henry unable to put his faith in the Machine God. By his hubris in fighting the glorious holy steam machine is struck down by the Machine God. This is shown In the Machine God's anger cursed mankind into performing manual labor forever for denying the Machine God's gift in the form of the Steam machine.

Or possibly John Henry wins and is blessed/cursed and turned to the first Servitor

The Chaos Gods are the reincarnations of the Emotional Entities.

 * Khrone is both the Butcher and Ion, since he's the god of hatred and bravery
 * Tzeentch is Adara, being hope
 * Slaaneesh is both Ophidion and the Predator.

The Emperor and The Chaos Gods are not evil counterparts to each other.
The Chaos gods are already Evil Counterparts to each other, due to the natures of chaos-- Nurgle/Tzeentch, and Khorne/Slaanesh, though none of them really get along, being, well, Chaos. The Emperor is sometimes thought to be the good counterpart to them collectively, being the Superego to the Chaos' Id, but when you think about it, the Tyrannid Hive Mind is a better candidate as his Id/Evil Counterpart. The EMPRAH is an intelligent, reasonable individual who wants humanity to grow infintely across the galaxy and eventually the universe (not necessarily opposed to Xenos so long as they stay out of humanity's way). The Hive Mind is a mindless, completely unreasonable collective (even to Chaos itself) whose instinct tells it to reproduce and eat all that lives until nothing remains but (due to the fact that the tyranids are basically one psychically-linked organism) It, in both the Materium and the Immaterium. The Emperor shines like a light in the warp (the Astronomicon) while the Hive Mind is a Shadow in the warp.

Angron's followers on his home planet had already been tainted by Khorne.
The past few HH novels are reconstructing the Emperor as not so much of a dick. Following this trend, it will be revealed that when he discovered Angron, his freed-gladiator followers had already been tainted by Chaos. It makes perfect sense, they were furious at their captors for forcing them into the Arena, they had already spilt blood. The Emperor saw this and knew they were beyond redemption, pulling Angron away from them and leaving them to die. Angron, being a stubborn bastard and a Primarch to boot, had not yet been corrupted.

Adam and Lilith In NGE are two lost Primarchs.
They were so thoroughly mutated by the Warp that they have become super giants with some inhuman features and unimaginable powers eclipsing even other Primarchs, the Emperor himself, or possibly other Chaos Gods as well.

The Enderverse is the prehistory of 40K.
Think about it: at the end of Children Of The Mind, Ender and his friends discover a method of FTL travel that involves traveling "Outside" the physical universe to a place where souls come from, and to which they return when a person dies, and in which dreams and fantasies can take on real form. Doesn't that sound kind of like the Warp? As a result, humanity's expansion through the galaxy increases exponentially, right up until the moment when disturbances in "Outside" cut off FTL travel. Before that happens, however, humanity's encounter with the Descoladores, and difficulties in relating to the restored formics, lead to humanity rejecting the Hive Queen and the Hegemon; paradoxically, Ender the Xenocide is rehabilitated as a hero. The formics are also changed, and become the Tyranids. The pequeninos, meanwhile, are able to acquire human technology and start advancing very rapidly (they of course eventually wipe out any humans on their world) and become the Tau.

The Lost Primarchs were sent through Time, not Space
Given the nature of the Warp, this is definately possible. My personal Pet theory is that one of the Lost Primarchs was sent into the far flung future of the the Grimdark future and the other was sent into the Past and might in some way be responsible for the Birth of the Emperor.
 * One of the Lost Primarchs is the Emperor himself!

Warhammer 40000 takes place in a literal Hell.
Because honestly, what word better describes this universe. It's a hell without end. Of course, this means the God Emperor is Jesus, and the Great Crusade was the Harrowing of Hell. He died for your sins!
 * The Chaos Gods are the Horsemen of the Apocalypse. Khorne is War(because of how Ax Crazy he is), Tzeentch is Conquest (he's a huge Magnificent Bastard), Nurgle is Pestilence (Papa Nurgle loves all living things, including pathogens), Slaneesh is Famine (his/her worshippers are starved for more and more pleasure), and Malal is Death.
 * There's only supposed to be four horsemen and Pestilence is an alternate name for Conquest.

Warhammer 40K is the future of Starship Troopers
Think about it, humanity is just beginning to expand into the stars, there are psychic humans and brain bugs, plus the power armour in the books could later evolve into space marine power armour (or downgrade into it). My guess is that it takes place just as humanity begins to expand into the stars in the very beginning of the Dark Age of Technnology.
 * Yeah, that would be downgrading. The amount of firepower worn in the book makes 40k look subtle. The primary weapons were nuclear missiles, they also had conventional explosives, and they had much longer-ranged flame weapons than are in 40k.

Eventionally, the Tau are going to rule the Galaxy
As the only people in the entire Milky Way that actually are improving their tech, it stands to reason that given time, their reverse-engineering skills and technological prowess will trump of all the others. In only a short 6 thousand years they have went from "spear wielding people on planet not important enough for the Imperium to bother with" to "killing you with rail guns." The horrors of the Chaos, the determination of Man, the hunger of the Tyranids, the elegance of the Eldar, the Dakka of the Orks can deal with the Tau now, but about in a thousand years, or the next ten thousand?

The only thing I can see the preventing the Tau from doing this is how far they will take the "Greater Good," although considering how badly #@$^ed the rest of the universe is, taking it over may actually be for the best.

Malcador was the man behind the emperor
Look at what Malcador did, he formed the Officio Assassinorum, he created the Grey Knights, he formed the Inquisition, and he was constantly by the emperor's side, all around the time of the Horus Heresy. My theory is that the Emperor was indeed a competent leader, but his relationship with Malcador was different than commonly believed, with the emperor being more like the face to the Imperium while Malcador focused more on organizational needs of the Imperium. In effect the Emperor was just a puppet, with Malcador pulling the strings.

The Human Race in 40k is actually a group of Chaos daemons, while the Eldars are actually our descendants.
The Eldars are the descendants of modern human (aka the original Old Ones), revelling in their superior technology inherited from us, and made more beautiful and intelligent, and given great Psychic Powers thanks to generations of genetic engineering. Just prior to the zenith of Eldar civilization, their experiments with Hyperspace (hence the Webway), along with how their psychic lives are dominated by scientific rationality (rather than religious paranoia), created the first Chaos God of Order, the Emperor. The Eldars were so proud of belonging to the (super)human race, the Emperor and his daemons took after the (flawed) appearance of the Eldar and believed themselves to belong to the Eldar as well. Unfortunately, the Eldar's Brave New World became so decadent they forgot their human origin, while the Emperor left the decaying civilization and formed his own new empire, firmly believing he and his daemons are real humans, not those crazy hedonistic humanoid aliens. Then the Emperor was weakened from a wound by a huge battle with Slaanesh, resulting in many of his Greater Daemons (the Primarchs) killed by other Chaos gods and replaced with the moles plotting to overthrow the Emperor from the inside. The actual daemonic of the Imperium is why the Imperium is as paranoid and Ax Crazy as other Chaos Gods in the first place. How about the history of the Imperium? Either it is all a lie fabricated by the Emperor, or he changed the past.
 * Seeing as how the Eldar have histories dating back millions of years, the Eldar must have sent themselves back through time at some point.
 * Also, Dark Eldar used to be the 40k equivalent of the Corrupt Corporate Executive, exploiting lesser species and fellow Eldars for fun and profit. What would later become Dark Eldars enslaved so much creatures, spent so much, and were so greedy that they gave birth to Slaanesh and destroyed the civilization. Then, Dark Eldars have lived their lives of unthinkable depravity, just as much of the real life upper class do today.

Eldar and Old One time travels had messed up the galaxy and created hell of a lot things out of the blue.
In one time travel, several Eldars were lost in the distant past in a distant planet. They eventually became the ancestors of Mankind. It is why Eldar and human look so similar in spite of their distance from each other. In other planets in the past, other Eldars were infected by some fungi and became the prototype Orcs. They also gave birth to the Tau, and so much humanoid races.

Dark Eldars are a metaphor for the Real Life Corrupt Corporate Executive and evil leaders, the Fall of the Eldar how the human civilization collapses for good.
The corruption, overconsumption, and dictatorship of the upper class (represented by the decadence of the Eldar) results in environmental damage and society falling apart as unemployment rate hits 100% and everyone save for the upper class starve/are tortured to death while machines do all the work. Then, the Earth has deteriorated so much that it cannot support any life (the Fall of the Eldar). The Seers, representing scientists and anyone with wisdom, predicting such grimdark future, realized they couldn't prevent such disaster and therefore humans faced a And I Must Scream fate. They all went crazy and disappeared one day, never to be find even in the Warp.

Tzeentch is Sun Tzu.
It's obvious.
 * More like Sun Tzu is a Tzeentchian Daemon Prince.