Channing Tatum is Gambit. But the only X-men related character I'm even slightly interested in at the moment is Deadpool
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Iron Fist has been case, according to Luke Cage (Mike Colter), but he said something along the lines of him being locked in a basement and not having his identity revealed.
on a "completely?" unrelated note, Scott Adkins (white martial artist) has been cast in Doctor Strange... role unknown. take that as you will. Feige said that TV and Movies will cross over sooner than we think, and Doctor Strange is his pet project. I'm not trying to put 2 and 2 together here (well... maybe I am), but it's just such a coincidence.
Spider-man's solo act will be a Highschool centered movie, probably Freshman, as they want him in HS for a while. They will not be doing another "origin" story, but that doesn't mean it won't be covered. He will first appear in Civil War, and we can only hope that they got him on a movie and TV contract so he can do the Netflix (and ABC) series as well.
Other than all that, I don't think we know much of anything about what his solo movie will be.
edit: so what have you heard Mr. Hollywood!?