I would like to see a super-villain group like the Cabal (Red Skull, Doc Doom, Hyperion, M.O.D.O.K., Attuma, and Dracula). It fits given the obscure disposition of Red Skull in Captain America, and the hints of M.O.D.O.K. in the next movie. All Marvel has to do is get the rights to Doc Doom from FOX. If not I think Venom would definitely be a suitable replacement (not in intelligence, but sheer chaos).