They could easily include Gambit and Deadpool in a future X-Men team movie without recasting and retconning the Gambit/Deadpool that we saw in Origins. if this was the comic-books, this wouldn't be a big issue, in fact a lot of things like this happened in the comics.
X-MEN RI5E' MUTANT OF THE MONTH | WOLVERINE | PORTRAYED BY HUGH JACKMAN
"You called that a landing?" - X1
"I thought I was just an animal, with claws" - X2
"Once you cage the beast, the beast gets angry" - X3
"Patience isn't my strongest suit" - X4
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