In an interview with CBR (who seem to have all the exclusives nowadays), Brian Michael Bendis has announced that he will be stepping down from all three of his Avengers titles for Marvel. That means he'll be off Avengers, New Avengers, and the movie tie-in Avengers Assemble. Until that time, he still has a good year or so of stories, and is looking to wrap up as many of his slow-burning stories as possible. Among stories he wants specifically to deal with are Norman Osborn & Protector's grudge with each other, and Red Hulk's membership - but with eight years of stories to draw from, he'll have no shortage of characters to deal with next year. Bendis has been writing Avengers since 2004, you guys! That's one heck of a long time.
The Avengers/X-Men crossover will also be coming next year, and it sounds like Bendis will be collaborating with artist Brandon Peterson for Avengers 24.1 around that time - which may well be connected to the event. But it might not be! The details are being kept under wraps for the moment.
Dropping these three titles will presumably give Bendis more time to concentrate on his other projects - Ultimate Spider-Man, Powers, and Moon Knight, amongst others.
The question is - who could possibly follow on from Bendis' legacy? The only person we can think of is Mark Waid...