5. X-Force
Talent attached: Jeff Wadlow, Mark Millar X-Force would offer Fox the opportunity to ensure the X-Men series' survival by introducing a 'Phase 2' where Jackman's Wolverine is quietly retired, the original team of mutants have their arcs wrapped up, and a whole new generation of X-Men are introduced under the guardianship of Mark Millar. Wolverine could certainly be involved on the sidelines here, Deadpool could be re-introduced as a litmus test for his own Solo film (discussed here later), and audiences might just fall in love with the likes of X-23, Psylocke, Bishop, Domino, Warpath and Cable. An X-Force movie would be an appropriate reboot for the whole franchise and a new strand of continuity could be established. A perfectly clean slate for a whole new host of movies with some familiar nods to the past to assure audiences. Jeff Wadlow is apparently attached as director here, and based on your opinion fo Kick Ass 2, is either a perfect choice or the worse think to happen to X-Men since Brett Ratner. This would be the first opportunity for Mark Millar to really flex his muscles as The Godfather in the X-Men series (it's more likely his hand will be apparent in the rebooted Fantastic Four coming next year), and sent the whole series in a tonally different direction. X-Force are generally seen as being more aggressive and militaristic, so we could easily see the whole Superhero re-defined again as it was thanks to Singer in the 2000 original.
Likelihood (out of 5): 5