That would be an interesting twist, considering how long Knull has apparently been around. Plenty of time for him or his offspring to have visited Earth in the 1,000,000 BC era and taken on the first Avengers.
Hmm, I think a lot of the issue people have with the multiple Hulks, Spider-People, symbiotes, Iron People, etc. is what TV Tropes describes as "uniqueness decay," or in shorter words --- it feels less "special" when there's more than one (or maybe two) of them.