I wouldn't be surprised if the multiverse only factors into this phase of the MCU and then they merge the timelines kinda like how arrowverse did.
In fact now that I think about it, that's happened in DC comic verse many times. They have the timeline story where stuff gets merged together.
It happens in marvel to a lesser extent such as the Age of Apocalypse storyline when Xavier got killed and then characters from that timeline came over into the main marvel universe.
Speaking of... I need them to do Nate Grey on the big screen. X-Man was one of my favorite comics.
do it Feige, please.