Speaking to IGN, Marvel Studios President Kevin Feige was asked about the possibility of having the upcoming Guardians of the Galaxy and The Avengers in the same movie.
"I don't know. Part of the fun of the comics is that could happen. Any character could interact with any other character because they inhabit the same time period and the same universe."
The conversation then shifted to the bug thing that links the majority of the MCU, and that is driving fans insane, Thanos.
"And certainly it is the inclusion of Thanos most specifically that is a declaration to audiences who are paying attention that this is connected to those other universes. Part of the fun is that it could happen someday. I don't know when that would be. Or maybe I know and I'm not going to tell you!"
Well, Feige certainly knows how to tease people.
Finally the conversation went to the rumored Universal and Legendary Sub-Mariner movie, to which Feige gave a big "No", there are no studios currently developing a Namor movie, and going by the explanation he gave, there won't be one for quite some time, even at Marvel.
It’s slightly more complicated than that. Let’s put it this way – there are entanglements that make it less easy. There are older contracts that still involve other parties that mean we need to work things out before we move forward on it. As opposed to an Iron Man or any of the Avengers or any of the other Marvel characters where we could just put them in.
Source - IGN