I wouldn't be surprised if Fox's X-men make an appearance (or six) in the MCU going forward, especially with the focus on the Multiverse in this phase, as well as leaning into legacy properties (which NWH has kicked off in grand style!) But I agree that they aren't going to be the 'main versions' going forward (though I personally have a soft corner for the First Class cast and wouldn't mind if the Dark Pheonix version of the team could return).
In a way, having the X-men from the previous franchise show up would allow Marvel to cash in on (and the fans to enjoy) that nostalgia, while leaving them free to pursue a very different direction with their new reboot. To an extent, this seems to be what they've done with Spider-Man - by bringing Tobey and Andrew's Spider-Men and associated characters and mythologies into the 'expanded' MCU canon, it leaves them free to go in different direction with the MCU Spider-Man without having to retread the familiar beats and characters of the previous iconic films. Kevin Feige, for instance, said that the MCU Spider-Man wouldn't be taking on his own Green Goblin and Doc Ock, because the iconic versions of those characters from the Raimi films have now made their mark on the MCU anyway. It could well be the same for X-men - they don't need to retread the Xavier-Magneto conflict if we get to see Patrick Stewart's Xavier or Ian McKellan's Magneto, and the history they bring with them, even briefly in the MCU.