It's no secret that Marvel plans way in advance for the movies that they make. They are looking at least three or more years into the future for what they want to give their fans. They are constantly in discussion, so there's always a chance that little bits of info on those discussions are going to leak out. We've seen it happen before, so why wouldn't it happen again?
The studio is currently heavily focused on completing Phase 2 with Captain America: The Winter Soldier, Guardians of the Galaxy, and Avengers: Age of Ultron. They will then move into Phase 3, starting with Ant-Man, which is the only officially announced film at this point, but Doctor Strange will most likely be a part of it as well. I'm excited to see what else they end up announcing, but according to a report from Unleash the Fanboy, Phase 4 of Marvel's plan might kick off with a New Avengers movie.
The site claims to have a source at Disney who had this to say,
“It’s so incredibly early in the process, but unless Robert [Downey Jr.] makes an insane deal with these guys, they’re going with New Avengers.”
Downey Jr. is currently signed up to do two more Avengers films, but after that he may not return to reprise his role as Tony Stark. It will be interesting to see what they do with the character when Downey Jr. calls it quits. I've heard they would replace him to keep Stark in the films, but we'll see.
The site goes on to ask their source if the New Avengers story arc will follow the comic book series Avengers: Disassembled which left the superhero team in a Diaspora until they re-assembled as the New Avengers. I know that the comic arc includes Spider-Man and Wolverine, but don't expect them to show up in any Marvel-produced film.
So when [they] asked if the movie would feature that comic arc or if they will just include a new team of heroes, the source said,
"Well, you’ve heard the recent casting announcements. They’ve got a ton of great guys. Paul Rudd. Michael Douglas. Aaron Taylor-Johnson. Whoever they choose for Doctor Strange and the other new guys in Phase 3. They’ve got a lot of great guys to lead the new phase of the team. But that’s all I say. It’s really early."
As of right now this is all just a rumor so treat it as such. The site does have a track record of getting solid intel, though. It will be interesting to see what Marvel does end up doing with Phase 4, but it makes sense that at some point they would bring us a New Avengers film.