In a recent interview with Collider, Marvel Studios President Kevin Feige was asked questions alongside Guardians of the Galaxy director James Gunn about the upcoming film. They were asked about movie ratings, post credits scenes, etc. (if you would like to read the full interview, I'll link it here: http://collider.com/kevin-feige-iron-man-4-guardians-of-the-galaxy/ ). However given that GotG is only 10 days away, we already know a lot about the film, and what we don't know, we soon will. What I thought was more interesting were his thoughts about the future of the Marvel Cinematic Universe.
Firstly, Josh Brolin's Thanos will be in Guardians of the Galaxy (and not just as a voice), and that like most other Marvel actors, he is signed for a multi-picture deal.
Secondly, Captain America 3 and Thor 3 are both in development as we speak, and Cap 3 is further along in development than Thor 3, since it has already been confirmed and will be coming out before it.
Thirdly, he admitted that an actor for Doctor Strange has not be contracted yet, however it's safe to assume that they do have an actor in mind, and that he's just not officially cast yet.
In addition, when asked about a Black Panther or Ms. Marvel movie, he talked not about whether either movie could happen or not, but about juggling them in conjunction with the rest of the universe. He did say that Marvel was looking at dates right now in terms of how these would fit in with other movies of the Marvel Universe, but this seems pretty optimistic to me. He essentially said that these are both definite possibilities, they just have to figure out when and where they would go.
Finally, when asked about Iron Man 4, things seemed slightly less optimistic as all he said was that anything is possible, and that they have a lot of work with the Avengers 2 and Avengers 3 to do.
Ultimately, I just covered the things that apply to future movies, but you should definitley check out the rest.
Guardians of the Galaxy comes out August 1st.