The new title for the X-Men: First Class sequel, pretty much gives the entire plot away.
In a recent interview with IGN producer Bryan Singer divulges that the new movie will be called Days of Future Past and hints that, although it will be tied into the same concepts as the comic, the themes and ideas of the movie will take on other issues as well.
For those of you not born in the 80’s, the story arc for Days of Future Past encompassed Uncanny Xmen #141-142 and introduced a dystopian future where the failure of the present day X-Men to prevent the assassination of mutant hating Senator Robert Kelley, leads to the future mutant apocalypse (not to be confused with the Mutant; Apocalypse) where surviving mutants are either “slain” or rounded up into internment camps. Oh yeah, and the Sentinels rule everything… so there is that too.
Since the comic really revolves around Kitty Pryde and Wolverine, my guess is they will take massive liberties with the story telling, “exploring the X-Men universe” as Bryan Singer says. Here is hoping for at least Bishop and Cable, and of course the Sentinels, some of the biggest and scariest baddies in the X universe.