Something similar will be happening. As Kevin Feige said, when discussing A4, "there will be everything before, and everything after". I wish they could put an end to all heroic and villainous characters that have been seen through all 3 Phases, but guys like White Wolf, Spider-Man, and Black Panther will still be around for sure.
Considering that Infinity heavily inspired both Infinity War and Endgame, my educated guess is that the Terrigen Mist will play a part in "creating" the X-Men. It's truly going to be interesting to see how Marvel Studios intends to keep audiences 'hooked' after Phase 3.