As an MCU fan, I’m happy that the Fantastic Four and their Rogue’s Gallery can be a part of the MCU. The X-Men films will take a bit of finessing to bring into the MCU, because
- A. I don’t think you want to lose the genre/experimental vibe they’ve been going with since Deadpool/Logan (otoh, the main X-Men films are not going in a good direction), and
- B. getting the place of mutants in the MCU right is critically important, because if you get it wrong you get Inhumans and no-one wants Inhumans.
However, I strongly disagree with arguments that the X-Men should be in their own universe. Wolverine started as a Hulk antagonist, the X-Men met the Avengers in X-Men #9 and hung out with Spider-man all the time, various X-Men join the Avengers, etc. We know that these characters can work in the same universe because they have for a half-century.
At the same time, as someone who doesn’t like corporate consolidation, I’m not super-thrilled about every part of the deal that doesn’t have to do with Marvel IP.