People are selling the X-Force component of the movie short as Cable and Domino are both extremely important members, and in this iteration, Deadpool is added in and most likely Colossus. So we have four members fully realized and working together by the end of Deadpool 2, so the team was more than just a punchline. And both Negasonic and Yukio could easily join in the mix.
Going forward I think it would be cool if this team ended up as better than what we've gotten in the X-Men films, but that's not in anyway hoping for failure from those.
When it comes to people who want to see Psylocke back: that would be for the X-Men movies where she is already established, a bunch of random posts on this forum will not somehow make that happen, and her type of role has already been more than filled by Domino. I hope for more females on the team, but they should fill in different roles.
One of the only characters I could really see crossing over would be Quicksilver as Evan Peters has expressed interest, or failing that they could make a new version of Quicksilver as there are still a few castmembers from Kick-Ass who haven't played him yet.