Ruffalo recently spoke with Collider and said that the real issue here is that Universal still owns the solo Hulk movies.
As far as a Hulk movie, a standalone Hulk movie, Marvel doesn’t really have the rights to that yet. That’s still Universal’s property, so there’s that issue. That’s a big impediment to moving forward with that. Now I don’t think that’s insurmountable, by the way, but I don’t know where it’s going from here for me.
Wait a minute! Isn’t Hulk a part of the Avengers universe and, therefore, okay for Marvel to use? Yes and no, apparently. If what Ruffalo says is accurate, then it means that even though Marvel Studios produced The Incredible Hulk, Universal maintains distribution rights. Because Banner is also a member of The Avengers, though, he’s able to appear in these big superhero team-up flicks. It’s the same train of thought that allows Scarlet Witch and Quicksilver to appear in Avengers 2, while Bryan Singer also used the speedster in X-Men: Days of Future Past.
So, sadly, even if Marvel wanted to make another solo Hulk movie, it’s currently out of their hands. Perhaps they could come up with some agreement, like the one they made with Sony to include Spider-Man in the MCU. As of now, though, this kind of project is not in the current plan.
There already are a lot of moving parts in the forthcoming Phase 3. The first priority is Captain America: Civil War, arguably the studio’s most ambitious undertaking yet. In pitting Steve Rogers against Tony Stark, Marvel will adapt one of the most famous comic book story arcs for the big screen and juggle a huge slate of characters, including the newly minted Black Panther (Chadwick Boseman) and, presumably, the new Spider-Man. From there, it’ll all be about introducing the new slate of superheroes — Black Panther, Doctor Strange, Captain Marvel and The Inhumans. Then there’s Guardians of the Galaxy 2 and the last Thor film to complete before the two-part Avengers: Infinity War.
Though Ruffalo said he doesn’t know yet if he’s in Civil War or not, Hulk could theoretically appear in any number of these films. As the actor revealed, he has approximately four more films left on his Marvel contract, which means we’ll definitely see him in some capacity after Avengers 2.