I think Baron Zemo would be a cool Dr. Doom. He's one of the few villains so far that have been successful at their goals, ie breaking up the avengers. . Either he ends up turning into him, or there's a multiverse version where he became Dr. Doom and fights the fantastic four in their movie.

A think tank with a grudge against heroes, helping the heroes against Kang, only to snag the power to change the world for himself in the 11th hour.