What I would like for the XMen film coming out is all new characters but assuming they don't here's what I want, a mix of some old and some new because of the crazy **** Wanda did.
I want from OG xmen - Cyclops, Storm, Rogue, Beast
From Younger XMen - Professor X, Magneto, Quicksilver
From Deadpool - Deadpool, Negasonic Teenage Warhead, Colossus, and Cable
From others - X23 - the new Wolverine
Then you need to flesh out Gambit, Rogue, Ice Man, Jean Grey, Havoc, Night Crawler, Psylocke (though I wouldn't mind Olivia Munn coming back, I just would rather seperate that movie out of my mind) Jubilee, Emma Frost, Mystique, Toad, Pyro, Destiny, Sabertooth, Mister Sinister, Juggernaut (though I could argue bringing the Deadpool Juggernaut in) Blob,and others.
Would love to see solo or duo movies for most of the characters before a big one anyway. Like would love a movie with Cyclops, Jean, Wolverine and one with Gambit, Rogue, and Jubilee. The advantage to brining in established characters like Halle Berry as Storm is you don't need any real backstory, they're established, you just need to flesh out new relations.