Saiyuki/WMG

The art of Seiten Taisei in the elaborate robes is really foreshadowing of his Buddha form at the end of the series.
Assuming that Minekura uses this part of the original Journey To The West, and assuming that this appearance isn't just Rule of Cool, art such as this depicting the Seiten Taisei could be really far in advance foreshadowing of what Goku/Seiten Taisei will become upon the end of the journey (see the last listing on The Other Wiki for details on Sun Wukong's becoming a Buddha). My reasons are thus:
 * Whenever shown in this form, Goku always appears nearly fully grown (or at least, not as a child) and thus he must take this form sometime after meeting Sanzo, Gojyo, and Hakkai. So far, he hasn't.
 * Seiten Taisei is always shown in this form with the nyoi-bo, despite the fact that the Burial Extra shows us how Goku got the nyoi-bo when horsing around with Gojyo. Unlike the original Journey, he did not have it since his time in Heaven. In addition to this, at all points in the main series in which he has broken his limiter, he has not once summoned the staff to fight- possibly simply because he doesn't need it, but perhaps because in that berserk state, he can't summon it (similar to how Kougaiji states in the Saiyuki Saiyuubito that one cannot summon a fiend when the contract holder is not themselves, as he could not summon Engokuki while being mind controlled). Upon enlightenment, in which the consciousness of Goku and Seiten Taisei merge, perhaps he can summon it.
 * Seiten Taisei is almost always shown in this form with extra markings around his eyes, which have never been present at any other time he has been released. This might be some symbol of his enlightenment, similar to a chakra on the forehead of a god or Sanzo priest. In the cases where they're forgotten, it's likely early versions or Minekura forgetting them (it wouldn't be the first time; she forgot his normal inverted Ohm youkai mark on his stomach in at least one artbook picture, and even pointed this fact out).
 * The Seiten Taisei is wearing some form of scrollwork diadem but clearly not the limiter that Goku has now, suggesting he's gone beyond needing the limiter.
 * This picture from the Salty Dog V artbook, which arguably shows him in the very state of nirvana.

Hakkai will go blind.
Because it'd be incredibly ironic (at least, I think that's the word), because he's put a lot of strain on his remaining eye, and, most importantly, I'd find it hot.

Hakuryuu is actually... Goujun. Recycled.
Okay. Hakuryuu (also known as Jeep or 'the little white dragony lizard Hakkai has') is basically part of the group. Goujun is eventually brought into the group during the events of Gaiden, where he's Kenren and Tenpou's boss. During the standoff in Western Army headquarters,  What else would be so fitting as being what he had so much power over back in the good ol' days? Plus, it would explain why Hakuryuu is so fond of Hakkai- they were. Also, if he remembered all of this, it would explain why Hakuryuu is so helpful to the boys even though at least half the group tend to forget about him at times and annoy him to no end. Besides, it'd make a cool twist in the story!
 * I thought this was canon? I know that it's at least fanon, but I'm not sure if or where it was confirmed.
 * In an interview it was said "as Jeep is probably Goujun" so either she hasn't decided whether to use this or she's being diliberatly vague I think.

Sanzo will become (or is already) a Youkai
Because the whole 'kill a thousand demons' thing worked on Hakkai. And how many youkai has Sanzo killed? Um. Lots. And it would be pure Fetish Fuel for some people. So... yeah.
 * Word of God says that it's "negative energy" that causes that, not the actual act of killing; I think. But I agree, it'd be hot.
 * Yeah, I just read an interview with Minekura that states we don't need to worry about this happening... So, guess this is Jossed, huh?

The events of Gaiden will be revealed sometime during Blast!
Because how can it not happen? It would be one hell of a chapter. And it would just be pure, undiluted Awesome. (Besides, there's just not enough angst in Blast yet. Mwahaha.)
 * Given Ukoku's propensity for MindScrews (i.e., spouting off information about Genjyo's birth parents during their fight in Reload to throw him off balance), I can totally see him revealing information from Gaiden to try to shake the ikkou's confidence in their mission.

The Minus Wave is not an inevitable side effect of mixing magic with science.
In the very first chapter, the Sanbutsushin claim that the forbidden technique of mixing youkai magic with human science in order to revive Gyumaoh is the cause of the Minus Wave, and explicitly compare it to how the children of youkai and humans are born cursed. There are a few problems with this.
 * First of all, Gojyo doesn't seem that much more cursed than anyone else in this series.
 * Secondly, Nii and Gyokumen are seen at one point gloating about how they deliberately caused the Minus Wave, implying that it wasn't something that simply happened.
 * Thirdly, Jeep showed up sometime before the Minus Wave, and extras claim that he's a product of such forbidden experiments as well (which also explains why he can, you know, turn into a car, an ability not demonstrated by any other dragon in the series).
 * Fourthly, the beings deemed "itan" by Heaven--Goku, Nataku, Homura--don't seem to be any less inherently capable of moral reasoning than anyone else. Yeah, they're powerful...but it's only when they're treated like ticking time-bombs that that power becomes dangerous.

Instead, the Sanbutsushin are either misinformed, or actively lying in order to prevent mortals from gaining too much power and becoming a threat to Heaven. Given the culture of Heaven we were exposed to in Gaiden, either option seems entirely plausible.

Sharak will die
How many other cool female characters have survived? TWO. My bet is that she goes psycho and Sanzo has to kill her, or she dies saving the ikkou. Either way, she's toast.

Sharak is a literal arhat.
A kind of alternative to the WMG above. Sharak introduces herself as "The 28th of Arhat" (as opposed to Genjyo's "31st of T'ang"). In Tibetan Buddhism, an arhat is a being enlightened enough to predict the time and place their next incarnation will appear. The best known real world arhat would be the Dalai Lama, who is believed to be the 14th successive incarnation of the same being. There are dozens of arhat lineages of varying authority in Tibet. Hence, succession for the Koten sutra may go by reincarnation instead of by master-disciple transmission, perhaps explaining how the Koten line has survived despite being MUCH closer to India and Gyokumen Koushu's minions than the Seiten line. OR...

The Koten Sutra's power has kept Sharak hidden from Ukoku
Sharak is thousands of miles closer to Houtou Castle and the Minus Wave than Koumyou was at Kinzan Temple, and than the unnamed Uten Sutra sanzo was when he was killed, yet she's survived to the present day. Yes, part of it may be that she's holed up in a heavily armed fortress at ~11,000ft elevation in the middle of the Himalayas. However, it may also be because the Koten sutra governs "the unknown and the ineffable". She may be able to conceal the location to some degree, enough at least that Ukoku and Gyokumen haven't been able to pinpoint it yet.
 * As of Shot 4 of Blast, PARTIALLY CONFIRMED. Sharak explains the power of the Koten sutra as "defense"--more or less a kekkai as in X/1999--rather than "the unknown" but confirms that the Koten is the only reason Tibet is still at least partially inhabitable by humans. In order to protect an area that large, she has to have resonators in each village (the vajra of the local shrines, it looks like) and cannot herself leave the immediate area without inactivating the kekkai.

One sanzo will end up with all five sutras
Related to "Sharak Will Die". We're down to 3 sanzo priests: Genjyo, Sharak, and Ukoku. Sharak's clearly been fighting for her life for quite some time now (she's got an impressive collection of scars even by Saiyuki standards), Genjyo is on a virtual suicide mission, and Ukoku "never feels alive unless it's eat or be eaten". Sharak's chances, as a named female character, are slim. There will be at most one survivor from Genjyo and Ukoku's showdown. Chances are there will be ONE surviving sanzo with all five sutras...which we've been told is a recipe for disaster (remember, living sanzo priests are supposed to split up to reduce risk, even when only carrying one sutra at a time). OR...

The age of the sutras, and of the sanzo priests, will end
Related to the WMG above. There are currently only 3 out of the required 5 sanzos, none of whom seem to have acolytes standing by to take over for them (unlike, say, Goudai training novices who hope to become sanzos or Koumyou having Koryuu in place to succeed him immediately). According to Ibun, this problem did not exist 40 years ago. Ever since Genkai's untimely death, the life expectancy for current sanzos has been plummeting. When it comes down to a confrontation between Ukoku and Genjyo, dark and light, is one going to be able to overpower the other or are they going to end up in some sort of stalemate or mutual destruction? Without anyone left to bear them, the sutras may change into some other, less dangerous form that does not require a human bearer, marking the End of an Age (and likely the end of Shangri-La's peace and stability as well). We're told that when more than one sutra is in close proximity, their powers can combine into something completely new and different. All five together could be...explosive.
 * Ooh yay, stuff go boom! And what strikes my mind is an image of Ukoku throwing back his head and laughing while he's engulfed by the resultant fireball. (He's crazy enough.)
 * For sure he's crazy enough. "HEY KOUMYOU I FINALLY MANAGED TO DIE!"
 * And can you imagine them greeting each other in the afterlife? I don't ship them together, but I can't deny they have a fascinating dynamic.
 * I have to think Ukoku would be greeted by Koumyou bouncing up and down on the balls of his feet and singsonging, "You~ owe~ me~ a~ suuuuuun~!"
 * Ahahaha. But that just brings up questions to me of what exactly their bet was, and how they EVER expected the winner to claim his prize.