I don't feel like Mystique should get her own film. She and Quicksilver should get their own X-Factor team.
The only characters who I can see getting solos are Wolverine, Deadpool, Gambit, Storm, Rogue and Cable. Even then, I hope that Gambit's film is one-and done. The X-Men franchises are all about teams. Fox should focus most on getting the newly assembled X-Men team a new film as well as get X-Force and New Mutants off the ground.
New Mutants should be a backdoor TV pilot and X-Factor should only get one or two films before the cast head to TV. X-Men and X-Force should remain on film and rotate which franchise gets a film yearly with an occasional solo film thrown into the mix. Legion and Hellfire should eventually get cancelled to make way for New Mutants on Fox and X-Factor on FX. FXX should get Alpha Flight who will hopefully be introduced in Wolverine 4.
I'm fine with a film using Mystique as the POV character but it shouldn't be a solo. I'd make the X-Factor film revolve around Shatterstar, Spiral and Mojoworld. The roster would by Mystique, Quicksilver, Rictor, Polaris, Strong Guy and Multiple Man with Val Cooper being the character Mystique is relating the story to.