2) Iceman
Like Rogue, the fact that Iceman was seen in that new timeline at the end of X-Men: Days of Future Past will make it difficult for Bobby Drake to rejoin the X-Men any time soon. It’s a shame too, because we only got a glimpse of how the heroic character should be portrayed in that movie, as he went full on Iceman and started sliding around the place, which he never really did in his rather tame appearances in X-Men and X2: X-Men United.
Recent comic books have seen Iceman use his abilities in inventive new ways, growing to the size of a skyscraper and basically being portrayed as one of the most powerful mutants in existence. Chances are we could be waiting to see Iceman until a reboot somewhere down the line, though that long rumoured X-Men 4 would certainly be a pretty cool (pun intended) to place him.