If we talk about Marvel Superheroes, there will be a lot because Marvel has known the Multiverse since the Loki series final episode. Not only from the Marvel Cinematic Universe, but also from the X-Men universe, the fantastic four universe or it could be the Spider-verse.
Rumor has it that all the universes will become one after the events of the secret wars that will occur in the MCU phase 4 or 5 later. If all the Marvel heroes can unite of course the Super Villains will too.
You can’t imagine how chaotic the Marvel universe will be in the future. Let’s see what Kevin Feige will do with this theory.