As some others have said, I think the X-Men films going forward will be relatively self-contained, kind of like the Guardians movies. I wouldn't be surprised if we see an Avengers film some time after the X-Men have been introduced that does not include them or any other mutants. Kind of like how Age of Ultron didn't include the Guardians. Then in another 10 years or so there will be the next big Infinty War style crossover movie, and that's when we get the Avengers / X-Men team-up. I'm curious to see how they do it. I expect at least a trilogy of X-Men films, and at least one more Deadpool film.