I couldn't care less about "box office reasons". I suspect that, for the foreseeable future, the MCU will always have their films above water. They're likely to maintain enough fanboys and fangirls to rake in the cash.
The X-Men fit. Especially with the Avengers disjointed and Nick Fury seemingly in space. I've been so distant from the X-Men franchise that I'd welcome a new team over seeing a 5th Avengers film. Unless, of course, it's X-Men vs The Avengers...
Carol Danvers is a boring MacGuffin byproduct. The X-Men, as a team, are not. I want to see heroes overcome adversity. Not use their Infinity Stone powers to defeat any purpose of potential storytelling.