I think we can now assume that the original X-Men trilogy, First Class, X-Men Origins: Wolverine, next year's The Wolverine and 2014s X-Men: Days of Future Past are all going to tie into together.
With Patrick Stewart and Ian McKellen already on board for Bryan Singer‘s First Class follow-up, Hugh Jackman is now in talks to return as Logan/Wolverine for Future Past.
My conclusion is that you simply can't have an X-Men movie without Wolverine.
So far, it is only known that Days of Future Past will be based on Chris Claremont and John Byrne's comic book storyline that ran in Uncanny X-Men #141 and 142 back in 1981. The story introduced the idea of an alternate future for the Marvel mutants that grew out of the Brotherhood of Evil Mutants killing an important senator, leading to a future where all mutants are held in concentration camps while giant robot Sentinels patrolled the land; most of the X-Men had been killed.
We'll have to wait and see if Jackman will have a small cameo or a more integral role in the film The cast also includes First Class actors Michael Fassbender, Nicholas Hoult, Jason Flemyng, Jennifer Lawrence and James McAvoy.
X-Men: Days of Future Past reportedly commences filming in spring next year and will open on July 18th, 2014.
Source: THR
