7) Death
There are two characters who have a relationship with Death: Deadpool and Thanos. The latter being part of The Avengers franchise surely wouldn’t mean Fox can’t introduce a version of a character who is essentially just a female Grim Reaper, and as nuts as it would be to see the Merc with the Mouth chatting away with Death herself, there’s no doubt a way of utilizing her in the sequel in a way which works.
Because Deadpool can’t die, Death is in love with him, and so Wade sets out to try and lose his healing factor so that he can finally be with her. There’s been arguments made over the years that Death is a figment of both Deadpool and Thanos’ imagination, but either way, the character looking to rid himself of his healing factor so he can finally die and escape his scarred existence could make for surprisingly powerful material on screen.