Marvel could play the game that D.C. did, for one of their many mega-crossovers. That is, claim that most superpowers in Earth natives are the result of the manifestation of a "meta-gene", which some individuals have, and others don't. You need this gene, plus a "triggering event" (lightning...
Kraven doesn't need to be a "take over the world" type supervillain. Harry's almost guaranteed to put on the Goblin suit, regardless of who is the "guest" heavy. On the other hand, it is not clear how Kraven would contribute to character development of Parker/Spider-Man in the way that Goblin...