There’s also the possibility that Sony’s Marvel universe could be retroactively made to exist within the main MCU continuity, but considering Kevin Feige’s wording about Spidey crossing cinematic universes, I suspect that won’t be the case.
Considering that Doctor Strange and Avengers: Endgame have already established the multiverse and parallel realities (plus Mysterio lying about being from another Earth in Spider-Man: Far From Home), enough comic book-y groundwork has been laid that Spider-Man could be thrown into another universe.