If they remain popular in Deadpool 2 and have some on-screen chemistry with Cable and Domino, they might turn up in larger roles in the upcoming X-Force movie.
By preventing the movie from turning into Deadpool and the X-Men, the writers leave open the possibility of more cameos and team-ups in the future.
However, it’s important to remember that Colossus has spent some time as a member of X-Force and Negasonic’s powers in Deadpool were borrowed from Cannonball (a founding member of X-Force).
It’s possible that the mutants’ roles in Deadpool 2 may still be in flux, considering that the movie is still in pre-production.