I don't think that Feige would go that far. Also, Feige and Marvel Studios have big plans for Phase 4.
Having a multiverse would make it a billion times easier to introduce more characters (especially later on the Fantastic Four and the X-Men).
Yeah but multiverse plots can get kind of convoluted and confusing. If they do that I'd prefer they do like DC and just have Earth-1 and Earth-2 as opposed to introducing different earths every movie.
Maybe Earth-1 is the "main" universe we know and Earth-2 is where the FF and the X-men are.