Marvel Studios boss Kevin Feige confirmed the eventual arrival of San Diego Comic Con's Hall H , coyly telling the audience that "there's no time left to talk about mutants, and how mutants fit into the MCU." The included release dates for movies and Disney+ TV shows through to 2021, but there is still plenty of Phase Four that remains shrouded in mystery.
The X-Men, along with the Fantastic Four, came under the same umbrella as the MCU when confirmed that a Fantastic Four movie is on the way at the end of Marvel's SDCC , but didn't go into detail about either of the formerly Fox-owned Marvel properties. Given that Marvel wasn't able to start work on them until the deal was concluded, we probably won't see either the X-Men or the Fantastic Four the MCU for several more years.
The Marvel Studios Hall H officially announced five MCU movies with release dates: Fantastic Four movie - and the comment about mutants came at the very end of this laundry list. It's worth noting that Marvel will soon have a lot more time to talk about projects, since Disney convention D23 is on the way in August.
Fox's X-Men franchise recently came to a close with the release of The New Mutants, which has had its release date pushed back multiple times and is now expected to release in 2020. It's hard to say goodbye to the versions of characters that we've gotten to know over the past two decades, but the X-Men franchise is probably in as good a position as it'll ever be for a complete reboot.
Marvel fans shouldn't expect to see X-Men in the MCU before 2022, and given all the sequels in the works it will more likely be 2023 or later. Still, it might be a good thing to let the property breathe for a few years before reintroducing the X-Men. Hopefully we'll find out more details about what to expect from the next incarnation of mutants at D23 next month.