Originally Posted by Mrs Vimes
Alternate future was what I thought of as well. Apart from it being the easiest option, to me it seemed that placing the Sentinel future post-X3 kinda deals a crappy hand to the X1-X3 characters. Once you change something in the past, either their whole timeline ceases to exist, or the action creates an alternate (reboot?) timeline with the alternate versions of the X1-X3 characters. So every time I'd watch X1 or X2, it would be kinda depressing to think that all those characters have nothing much to look forward to, and that Professor X's dream of coexistence eventually comes to nothing, in this timeline.
Judging by the most recent comments though, it seems that DoFP is set post-X3 after all.
if the idea is indeed that after this film everything that happened in X1,2 and 3 would be changed then that would be very tricky to explain at the end of the film and would make complications to have to explain