To LOVE-Ru/WMG

Mikan called Rito by his name because of her repressed attraction.
Sometimes in their childhood Mikan confessed to Rito or telling other people about her crush and get a reply that she cannot marry her brother. Hence Mikan calling him in a First-Name Basis to make some distance between them, this behavior continues to her puberty even though she know it's hopeless now (she think).
 * Although it may also related to Spiral's case of Blade Children Incest (see the Spiral section on this page, It Makes Sense in Context).

Golden Darkness is Eve from Black Cat.
Not long after the events of Black Cat, the Deviluke Empire invades the Earth-like planet the series takes place on and takes over without much trouble. In the chaos of the invasion, Eve is separated from Train and Sven and somehow stricken with Laser-Guided Amnesia that erases all memory of the previous year or two of her life. With her only remaining memories being her time in service to Torneo, Eve begins making a living doing the only thing she knows how to do - hunting down and erasing targets for cash. Her extraterrestrial contacts take her off-world, where she becomes the infamous Human Alien assassin we all know and love.
 * Pretty much confirmed. Same dress style, same voice actor, same mother, same nanomachine-based powers, same origin,.

Lala is literally sent from Hell to ruin Rito's life.

 * Consider the name of her race; Deviluke.
 * The heartwarmingly normal Episode 14 showed what his life could be like without all the madness and terror from outer space. Heck, his happiness with Haruna-chan would be faster achieved without it.
 * Enter into an unwanted and loveless marriage away from the one you love, or watch the earth get obliterated? A Sadistic Choice that only demons would be cruel enough to force a mortal to live through. Lala is playing along, and so she is no more innocent than her tyrant of a father.
 * It becomes clear fairly quickly that, while he may not admit, or even fully realize it, he does love her at least as much as he does Haruna. Lala makes no secret of her feelings towards Rito and its made very clear that her feelings are genuine.
 * Of course, the last chapter of the manga notes that once Rito is ruler of Deviluke, he could do whatever he damn well pleases, including just marrying both Haruna and Lala. Note that it's Lala's idea.
 * Some of us would pay to have our lives 'ruined' the way she's 'ruined' his (Damn you Satan! You've cursed me with a gorgeous woman who likes to walk around my house naked and attracts fantastic adventures and other gorgeous women! Get thee behind me, fiend!). Although admittedly, Rito does seem unhappy a lot of the time... I guess that's just what happens when I Just Want to Be Normal meets Cursed with Awesome.

Rito is somehow related to Keitaro.

 * How else do you explain the fact that he isn't dead yet? Not to mention all the Accidental Pervert moments and accidental groping.
 * Perhaps he is actually the son of the Devilukean ruler, de-tailed by a vengeful enemy. The king, seeking to hide his heir, placed him on Earth with a childless couple who he rewarded by giving them the ability to have their own child, Mikan. Its why Rito has survived pert near everything you can name, and why Lala and her sisters were drawn to him, ala Luke/Leia. Alternatively, he is the king's expunged decent half, turned out so that he could be even more cruel and perverted. Not having this part of him was why his great battles drained him down to child status. It fits his perverted nature to have his kids hot for one another and not even realize it.
 * Or it's just because Rito is a Half-Human Hybrid, especially receiving genes from his father. A mangaka with godspeed drawing ability that makes his assistant dying of exhaustion, and having endurance that only devilukean can become sufficient assistant? C'mon!
 * If Rito were an alien he'd be as crazy-strong as Lala and Golden Darkness are.
 * Not if Rito were de-tailed. Lala's Dad is a Goku-homage, and perhaps any overt powers beyond endurance were lost when the tail was, as happens with Saiyajins' Oozaru ability.

Mikan's maturity will not survive early puberty
Their father is 24/7 on his manga, and Mom is pretty much the same in the world of fashion. Not the worst anime parents by any standard (Paging Mr. and Mrs. Hayate, Beyblade's Judy Tate, Mayu's Mom from Elfen Lied among countless others) but still not the most engaged. Rito was once a together athlete whose only lack was not confessing to Haruna, and he seemed on the verge of that. Then, he gave soccer up to care for a sister who can plainly care for herself--or can she? See, Rito, even in his denseness, knows that the Yuuki clan loses its sense of responsibility and many social skills once adulthood begins to kick in, and he wanted to be there for her as she fell. Evidence : At story's start, while always caring for him, Mikan is head and shoulders above her brother in almost all things, even knowing how he should handle girls better than he, and snickering constantly at his expense. Now she is a raging pile of bro-plex, teased by her friends just as he was, and noting that he really does rather well versus the insanity of life with Lala. Soon, any traces of the uber-fiend Ruthie Camden will vanish from her, and Lala will have her porting starkers into the boys' changing area, with her hair and eyes exploding while she stutters.

Yami is a lesbian.

 * She constantly attacks all the guys who do "ecchi" things, but when the girls start groping her, she just starts blushing. It's practically the only emotion she shows. Not to mention that she's constantly hanging around with Mikan, who, as we know, is incredibly sexed up for a girl of her age. Not the mention that the pairing would be incredibly cute.

It's not because of her brother that Mikan doesn't date.

 * Following from the above.

If/when To LOVE-Ru somehow resumes...

 * Then Haruna will be given either The Nth Doctor or The Other Darrin treatment. She's too popular to Brother Chuck or Put on a Bus, so she will be redesigned, perhaps literally by one of Lala's inventions, to divorce her aspect entirely from the artist's real-life ex-wife, who is said to have caused the situations that may have killed the manga.
 * Genre Shift to shounen?? perhaps Rito turned more Badass while Haruna,well....undergo Adrenaline Makeover to cope. Imagine Rito in last episode but taller, more mature, MORE BADASS, but not evil to further expand his Harem. Add "evolved" Haruna, leveled-up Harem and BadAss-ficated friends and you got To-Love-Ru IN STEROID
 * as for now, Jossed.

The spinoff will feature Yami as a main character.
Yabuki obviously has a fairly strong attachment to Yami/Eve's character, seeing how he's used her in two separate manga so far (three if you count her cameo appearance in Mayoi Neko Overrun) yet he didn't really do a whole lot with her in TLR. But notice how she's featured prominently on the promotional art for the new series, and it's apparently named "To Love Ru: Darkness". Assuming the source is correct, this would be a good way to alter the series' primary love triangle and get rid of Haruna by replacing her with Yami.
 * Well, Haruna isn't being replaced, but there does seem to be more focus on Yami than before.

Rito gets Badass training from Train
In the new spin off things become much more action oriented and Rito gets tired of depending of his harem of aliens to defend him and asks Yami for training but she says she won't, or can't, help but will ask someone else for him. She asks Train who accepts as a favor to her.
 * With the sequel being Darker and Edgier, and with Yami as focus, one can still hope this isn't Jossed.

Rito and Mikan are Not Blood Siblings.
Momo has no problem considering Mikan as a target of the "Harem Plan". Maybe she knows something the audience don't.
 * Or maybe she finds incest hot.
 * Considering the plan also includes both of her own sisters, that is highly likely. Or at least that it isn't a taboo subject for her.
 * It would be intriguing to learn if this is just another aspect of Momo's naughty nature that she tries to hide from others, or if Devilukeans in general don't have qualms about incest ... or perhaps that last only applies with royalty.

we will see some kind of MIB organization

 * A perfect Expy of Chronos and an interesting plot. Also, that can help to explain how the aliens do to integrate to society.
 * Well, Zastin's subordinates dress like MIBs, including the sunglasses, so maybe we've already seen such a group from the first.

Momo and Nana are half-sisters of Lala
It was stated that polygamy is legal in deviluke. the king love women. It was never stated that they had the same mother. any question?
 * Sorry, but no. Apart from the family resemblance that comes from their mother (it was mentioned early on that Lala takes after her mother in looks, and just looking at them will tell you the pink hair doesn't come from their father), at the same time it was said that polygamy was legal on Deviluke, it was also mentioned that Gid didn't have any other lovers than his wife.

Momo will be Rito's first wife.

 * Even though she is fine with any position, she is a bit greedy. Also, of all girls she is spending the most time with Rito, proving herself to be quite reliable.
 * Doubtful. The plan apparently only works if Rito is the king of the universe. In order to do that, he has to marry the first princess of Deviluke before getting extra wives, and that's Lala. Marrying Momo would not put ito into a position that would likely allow for polygamy, and would likely annoy Lala's father.
 * However, this does not preclude Momo being his first sexual partner. Of all the girls, she is by far the most aggressive in that area and is clearly determined to be one of his first at the very least.

Yami has the same drawback as Yuria

 * The first man she has intercourse with becomes her master, forever. That's why she is violently opposed to perceived male sexual advances, but only mildly protests much more deliberate harassment by women.

The manga has been canceled
Because Mangahere hasn't updated it yet...
 * Jossed repeatedly as of November 2014.

Rito will become king whether he marries Lala or not
Lala's mom is irresistibly beautiful, so much that she says no man but Gid Lucione Deviluke has been able to keep from being crazed with lust and attacking her if he sees her face unveiled. At the end of Darkness Chapter 49, Rito accidentally pulls off her veil and gets a good look. We're set for disaster unless he turns out to be able to restrain himself -- case-hardened by all the sexy craziness, or maybe that plus Mea's mind probes have done something permanent to his brain. At any rate, imagine that Rito resists the queen's overwhelming beauty. She reports this to Gid, and he notifies Rito that, having just proven himself to be the strongest-willed man in the universe, he's now the heir to the Deviluke throne. Not just prospective husband to the heiress -- he's replaced Lala in the line of succession. Lala is unlikely to be disturbed by this; Rito will be freaked out even more than he was before. And Momo thinks that now it doesn't matter in what order he marries the members of the harem ... and that being so, she wants to be his first.
 * Aaaaand Chapter 50 confirms that Rito IS able to restrain himself.