Joss Whedon had something to say on the topic of roster changes at a Directors' Guild screening of The Avengers
via marvel-freshman at voldemort.com
Although the filmmaker never revealed anything about Marvel's The Avengers 2015 sequel, he did acknowledge the importance of swapping characters every now and then. “I used to read 'The Avengers' and part of the ethos of the team was that it changed their lineup every month. Their 150th issue was just a bunch of faces. 'Who will be in the team now?!' We had the first issue as a poster in the offices. Now that I'm working on the sequel I said, 'Let's the second issue up there! Let's change it up a little bit!' The second issue is 'Introducing… Giant-Man! And this character! They were already changing it up after one issue. That's what they always do.”
This is the advantage of having a writer/director who is an actual fan of the comics: He understands the team dynamic and its tradition of constant evolution. It seems certain that we're going to see some new members in TA2. I'm hoping that this was a hint that Whedon will introduce Ant-Man & The Wasp, though the holdups in the Ant-Man solo movie may make this doubtful.