5. Jubilee
Another character who has to this point been limited to a series of non-committal, fan-servicing cameos, Jubilee is definitely worthy of having a meatier part in Days of Future Past, though Bryan Singer may have in essence shot himself in the foot a little, as it seems like many of her characteristics have essentially been transposed into Anna Paquin's character of Rogue, specifically her close, almost father-daughter relationship with Wolverine. This might seem to cancel her out to an extent, but she still has some fantastic powers which would look undeniably awesome in this universe. Able to emit blasts of energy - or as she calls them, "fireworks" - from her fingertips, she would add some much-needed kinetic energy to the team and allow them to function more cohesively. Who knows quite how she would figure in the narrative, but if she gets more than merely a peripheral role, then count me interested.