In the Spiderman trailer they officially introduce concept of multi-verse. If that doesn't spell "X-Men" I don't know what does. If they were to completely reboot X-Men, 5 years is not nearly enough. It's not a single character, it a whole race of people. It would be very difficult to retcon X-men into MCU, in one year or even five. But with multi-verse, the door is wide open, right now! Not rebooted X-men. They same x-men as they are now (actors, characters). Will they do it? Don't know. Can they do it if they wanted to? Oh absolutely.
Maybe, but won't it be fun, if my theory is actually true! The signs are there:
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Maybe it doesn't mean anything, maybe it stands for “mutant containment unit".... Or maybe it stands for MCU is coming, you can't hide from it!
Even if the MCU uses multiverse concepts to introduce the X-Men, even if they actually keep (some of) the popular actors because they don't think they can get anyone better, it will never be the same characters as the fox movies. The fox movies have never been as successful as the MCU and they (other than Deadpool) have been losing steam for years. They're over.
Also, Endgame, Dark Phoenix and Far From Home were all conceived and shot before the Disney/Fox deal was legally approved. It would literally have been illegal for anyone to include anything in any of those movies on the basis of the assumption that the deal was happening. They weren't allowed to act on any of this in any way until the deal was 100% complete (March 20).