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.
If they deal with Alt timelines, some version of the X Men will be screwed regardless if its post X3 or not. They would have to do a fixable future to get around that.