HitFix can confirm that Col. Rhodes, aka War Machine, has a key role in the conflict with Ultron that is the main focus of the sequel.
Really, it was all but confirmed when we posted the story initially, being that the source was Don Cheadle, but the part that interests me is the "key role."
Joss Whedon did an outstanding job of giving each of the Avengers their moments to shine throughout the first movie, so I'm going to trust him on this one. But I can't say a little worry doesn't creep in when you have Nick Fury, Tony Stark, Captain America, Thor, Hulk, Hawkeye, Black Widow, and now Scarlet Witch, Quicksilver, and War Machine all crammed into one movie, and with a new villain in Ultron to introduce. Avengers probably did the best job of any superhero movie to juggle so many characters in one movie so far, hopefully they don't push past the breaking point.
Marvel, and the guiding hand of Whedon, certainly seem to be preparing for what's ahead for them behind the scenes. With Robert Downey, Jr. looking to retire from the Iron Man role, Don Cheadle might make a good alternative temporarily, but eventually they will need to recast the role of Tony Stark and that's something Marvel hasn't really had to deal with yet. Sure they've recast the role of the Hulk, but neither those movies, nor the actors playing Banner, took off the way Iron Man and RDJ have. Cheadle certainly has the charisma, a different sort than RDJ certainly, to carry at least one future Iron Man movie, but eventually, they will need that new Stark.
The same could be said of Captain America and Thor, their individual movies have certainly been able to become main attractions on their own, but those actors will soon move on as well. They may not be quite as popular as Iron Man, but by the time their own trilogies wrap, they will certainly be in the same ballpark. Marvel phase three will introduce several new characters, some rumored and some confirmed: Ant-Man, Doctor Strange, Black Panther and more, with Avengers 2 introducing Scarlet Witch and Quicksilver, but does Marvel hope to replace the core line-up with new characters before recasting roles?
It will be interesting to see what becomes of the Avengers and the Marvel movie-verse as phase three wraps and Thanos rears his ugly head in what I assume will be Whedon's final Avengers movie and wrap the trilogy. By that time, all of the original Avengers actors may be at the end of their contracts and the landscape of Marvel movies vastly different and Joss Whedon ready to move on from Marvel. Will a movie Avengers have an easier time surviving with "b-listers" on the roster than the comic? Or, will it always come back around to the originals to carry the franchise?
Until then, replacing Robert Downey, Jr., a man who practically IS Tony Stark, will be the first and possibly biggest test for Marvel.