1) Sabretooth
Both Hugh Jackman and Liev Schreiber have indicated that Sabretooth could make his return in the next Wolverine movie, and that happening would be downright awesome.
Bryan Singer handled the character very poorly in the first X-Men, and while X-Men Origins: Wolverine was pretty terrible all in all, Schreiber’s awesome take on this villain and the chemistry between him and Jackman is impossible to fault.
As so many characters are off limits to Fox when it comes to adapting Old Man Logan, they’d be foolish not to bring back Sabretooth for Wolverine’s final battle, and if they really want to shake things up, they could follow the comic books by having him (sort of) decide to become a good guy and join the X-Men.
For the time being though, it’s absolutely essential that we get to see the definitive Sabretooth on the big screen come 2017.