Maybe they'd be better suited to just start an X-Force movie franchise based around Cable and the New Mutants, etc., and then can tie in the mainstream X-Men Film franchise as well as tie in characters like Bishop, Apocalypse, Sinister and The Marauders, and Stryfe and the MLF via time travel. They need to do a Days of Future's Past storyline on screen also. That could be the premise for the X-Force film (Cable goes back to save Jean at the lake to prevent the unleashing of Phoenix and her murder of Xavier which leads to the Days of Furtue's past timeline [Xavier going underground after transferring his consciousness into the body on Muir Island, leaving no leader for the peace movement amongst Mutants, and Magneto leading a successful assault on Washington DC], which subsequently leads to Cable's birth and an alternate timeline, but in this timeline Sinister comes to harvest Scott and Jean's DNA to create Stryfe/Cable).
Just an idea I've had of what I'd do with the movie, substituting Cable for Rachel in the Days of Future's past storyline.