Don Cheadle, who's replacing Terrence Howard in Iron Man 2, must be really glad to take over the role of Jim Rhodes aka War machine, because this is a hell of an opportunity for him: according to Bob Layton, a co-writer of the Iron Man comic book (whose notable input was War Machine), Warner Bros is king of thinking about a spin-off War Machine movie! Here's what Bob Layton said to MTV:
A spin-off War machine movie would definitely make sense: after all War Machine did get his own comic book, plus a spin-off would fit in Marvel's plan of greenlighting movies based on their characters. And last but not least, there's a real fan base that would eagerly go watch a War Machine movie. So i'm quite confident that in a not too distant future we'll certainly hear bout this War machine movie.
Moreover Don Cheadle, who's replacing Terrence Howard as Jim Rhodes aka War machine, is an actor with a lot of experience and a real charisma: so Don Cheadle's got what's needed for a lead role in a blockbuster.
But I guess it won't happen before the release of the Avengers movie , so still a few years before we can enjoy a War Machine spin-off movie.