10 MCU Characters Missing From Marvel's Phase 4 (And Why)
2. The X-Men
It's entirely possible that the groundwork will start being laid for the Fantastic Four to be introduced in Phase 4 (it is, after all, an appropriate number), especially after Kevin Feige directly referred to the team at Comic-Con last year. If you're waiting on the X-Men to start appearing following the Disney/Fox merger, though, you'll need to be patient.
While Eternals could drop some hints regarding how mutants came to be, Disney is looking to create as much space as possible between Fox's disastrous X-Men movies and the eventual reboot. That reportedly means it's going to anywhere from 4 - 5 years before the team returns to the big screen.
It's worth noting that Feige even referred to the heroes as "mutants" rather than "X-Men" at the aforementioned Comic-Con presentation in San Diego, so who knows if that moniker will even be used. For what it's worth, Marvel Studios Executive Vice President has said that using the word "men" in the team's name is somewhat antiquated given what a diverse line-up the group boasts!
However, while there are no plans for the X-Men, certain locations from their world will be used in Phase 4, includng Madripoor in The Falcon and The Winter Soldier.