Main WMG/XMenFilms guesses here.

[[WMG: In the movieverse, Emma Frost is Cyclops' mother]]
Well, she'd be way too old to be his girlfriend. And it kind of fits with the decision to make Havok his father instead of his younger brother. On top of that, it would be kind of amusing to see everyone's favorite snarky, [[WomanInWhite white]] [[{{Stripperiffic}} lingerie-clad]] {{Dominatrix}} become the mother of the guy that she's currently [[ParentalIncest sleeping with]]. Because, y'know...if you're going to annoy fans by messing with {{Canon}}, you might as well have some fun with it.

[[WMG: Xavier was always bald.]]
That's why he told Beast not to touch his hair because he was really wearing a wig.
* Maybe he uses his powers to make people think that he has hair.

[[WMG: Darwin is alive.]]
He's ''Darwin'', he can survive being atomized by a condensed plasma blast! He just needs some time to put himself back together.
* In the comics, he ''did'' survive having his body destroyed. He grew a new one.

[[WMG: Fill in the continuity holes here.]]
The movie has too many similarities to the other films to be a reboot, so what happened was...
* Charles regained his ability to walk before his appearance in ''Wolverine'' and ''The Last Stand'''s prologue, but lost it again before the original movie.
** Confirmed!
* Erik occasionally found himself on good enough terms with Charles to work with him, such as when they build the second Cerebro.
* Hank's cameo in ''X2'' was either old footage, an actor hired by the real Hank to make public appearances, or the result of a temporary cure.
** Confirmed to be that third one.
* The Emma Frost that appeared in ''Wolverine'' was a separate character from the Frost in this movie, perhaps her daughter.
* The young "Storm" and "Cyclops" in this movie were actually just similar-looking mutants.
* The reason Xavier was surprised by Erik's helmet in the first movie is because the original helmet had been lost for years at that point.
* The incorrect ages given by Charles in the first movie are the result of psychic tampering with his memories (perhaps by this movie's Frost, or even by himself).
* Emma Frost erases Charles' memory of the helmet, and possibly his memories of Mystique. She could have also erased Mystique's memories of living with Charles.

[[WMG: Lets pretend some legal troubles have vanished for a second.]]
I'm going to preface this WMG by reminding us that it is very, very unlikely due to film rights issues that we all know and love (Or can google and hate). So lets pretend Marvel Studios still owned the film rights to X-Men and that this movie was in continuity with the MCU. In that case I would venture a guess that the helmet that was given to Shaw by the Russians was not built or designed by them but instead found in an archeological dig. To be more specific the helmet was found in a ditch with a bunch of very large human shaped packs of ice and a single seemingly human skeleton that was wearing some shiny armor and holding a sword with the word "Baldur" written on it in norse runes. The helmet was merely given to Shaw because thems russkies knew he liked fancy stuff and he discovered its ability to block telepathy on accident later and lied about its origins because it reminded him of his old rival Johan Schmidt. Other fun ways we could tie first class into the MCU? List below if you want.
* Mystique's slowed aging could be used as the basis to introduce the infinity formula. Which then fell into Shields hands after Magneto broke into the CIA. Possibly using some on himself meaning they wouldn't have to recast MichaelFassbender for modern stories.

[[WMG: Magneto lived in Ireland for a few years.]]
Hence his having a noticable touch of an Irish accent - he learned to speak English in Ireland. It's also posible he was hunting [[NaziGermany Otto Skorzeny]] [[ who was living in Ireland at the time.]]

[[WMG: X-Men movieverse is an AlternateHistory in which JFK wasn't killed.]]
There are rumors that the ''Film/XMenDaysOfFuturePast'' movie will begin with Magneto killing JFK, explaining the bullet's weird trajectory. In the comics, BadFuture was the result of Senator Kelly being assassinated by the Brotherhood, but movie Kelly is too young to be important in the timeframe of the movie. So I think it will be like this: Magneto assassinates JFK, causing the BadFuture, which will have the actors from the original trilogy reprise different versions of their characters. In the end, JFK's death will be prevented using TimeTravel, thus causing the X-Men movieverse as we know it.
* Or, for a version with less AlternateHistory, the X-Men will still fail to save JFK, but will manage to cover-up Magneto's involvement, thus preventing the anti-mutant hysteria that caused the BadFuture.
* Jossed; In Film/XMenDaysOfFuturePast JFK is dead and the government believes Magneto killed him, but Magneto insists he was actually trying to ''save'' the president and someone stopped him. And the BadFuture is caused by Mystique killing Trask, not this.

[[WMG: The Man In Black is Fred Duncan.]]
In some of the earlier X-Men issues, FBI agent Fred Duncan served as the team's government liasion. The Man In Black isn't an FBI agent, but he serves a similar role in the movie. In the sequels, he could serve as the team's spy in the CIA.

[[WMG: Shaw wasn't actually killed.]]
The coin Magneto shoved through his head seems to have missed his ''medulla oblongata'', the part responsible for life functions. Shaw was left alive, but seriously wounded (maybe for life), dependent mostly on the common humans he scorned.
* He survived and became an actor who went on to play Anakin Skywalker in ''Return of the Jedi.''

[[WMG: Klaus Schmidt is related to RedSkull]]
The RedSkull from ''Film/CaptainAmericaTheFirstAvenger'' to be specific. His name is Johan ''Schmidt''. Coincidence?
* Actually, Schimdt is the German equivalent of Smith. It's one of the most common last names in Germanic states, so yeah it could be a complete coincidence.