5. The Incredible Hulk: The Leader
Towards the end of 2008's The Incredible Hulk we see Samuel Sterns, played by Tim Blake Nelson, undergoing the transformation into the Leader, a super intelligent Hulk villain from the comics, after coming into contact with Bruce Banner's blood. The original plan was to have Nelson return as The Leader in a sequel, but a Hulk sequel doesn't look like happening any time soon. A new Hulk film would likely go in a different direction anyway, meaning the Leader wouldn't be used at all. If Hulk is too busy with the Avengers to deal with him, why not leave it to Agent Coulson and his team? In the comics, he hired his own team of spies to steal information from governments, which would make a nice plot in AoS. Seeing two spies teams facing off, or trying to hunt something down, would be a different threat to the team that would make the series more interesting.