"The Avengers" is already out and became a huge success. Marvel Studios is raking in the cash and the Disney execs couldn't be happier! So whats the problem?
The problem, is what Marvel Studios should now do with this huge franchise. While "The Avengers" was great, there were some problems that it barely avoided. One of the major problems was the balancing of characters. There were only 6 heroes in the movie, and each of them barely got enough character development in order to avoid complaints. And even then, Hawkeye didn't get much development at all because of his "predicament". Had Hawkeye never been compromised, screen time among the heroes would've been even more stretched out. So how could a sequel to The Avengers, with more heroes, be just as critically successful as the first? It's going to be very difficult.
Come the release of "The Avengers 2", the most likely heroes to show up will be Ant-Man and Wasp. If a solo Ant-Man movie happens, Wasp will surely be involved. That's 2 heroes already! An 8 person Avengers roster will be hard to balance. But lets not forget the possible inclusion of other heroes like Doctor Strange, Ms.Marvel, Nova, and all of the other cosmic heroes Marvel wants to introduce. Obviously some of these heroes will be save for an "Avengers 3", but that still brings the same problem of too many characters in a movie.
In my opinion, the best idea for Marvel Studios would be to take out Hawkeye and Black Widow from the roster and add another 2 or 3 heroes to the mix to spice things; Ant-Man, Wasp, Nova, whoever Marvel wants. They should then take Black Widow and Hawkeye and either spin them off into their own franchises, or make a "Secret Avengers" movie with them and other heroes that Marvel hasn't used yet like Heroes for Hire or Black Panther.
All in all, Marvel and Disney need to be very careful as to how they go from here. Phase 1 was a success, but Phase 2 is going to be much more difficult to pull off. It seems as if they want to go pretty cosmic with their future movies which may or may not work with the general audience. The last thing anyone wants to see is "The Avengers 2" to flop after the amazing success of the first one. Between me and you, my fingers are still crossed that Disney pays Sony a visit and finds some agreement about a particular web-head.