Re: FoX Cinematic Universe
Honestly, my plan would be to use DOFP as the last hurrah for the original actors and that team line up and have it split off into two alternate timelines. Use the First Class timeline as the new starting point for the franchise.
Reintroduce Cykes, Storm, & Jean into the timeline as younger characters and probably add some new faces as well. Maybe do the Mutant Massacre storyline or one of the various ones with Mister Sinister.
I'd also start to world build the X-Men universe as well. There are plenty of characters that can carry a solo movie outside of Wolverine or other teams that are capable as well. X-Corp, Excalibur, X-Factor Investigations, The Shiar would all be cool.