8) Taskmaster
Unfortunately, Deadpool director Tim Miller recently revealed that the rights to Taskmaster have reverted to Marvel Studios. However, with them and Fox now seemingly on better terms than in the past (hence why those X-Men TV shows are happening), it would be nice to think that some sort of deal for this character to appear in the sequel could be made.
Capable of copying the fighting style of anyone he comes in contact with, the downside to that for Taskmaster is that his memories are constantly being wiped away by the new things he learns. Pitting Deadpool against someone who would essentially be his equal has a lot of potential and based on the many times these two have teamed up or squared off in the comic books, it’s fair to say that seeing them do so again in live-action would definitely work.
Having the Merc with a Mouth encounter other costumed mercenaries is a must now the origin story is out of the way, as it opens the door to loads of exciting storytelling possibilities.