The name is not being used right now. And Marvel likes introducing new characters under their trademark names. I'm surprised they haven't tried making a new teen War Machine like Ms. Marvel or Ghost Rider or Nova.
Apparently, the thought at Marvel is that the character's name is more villainous than heroic, hence the introduction of Parnell Jacobs, the villainous War Machine. It didn't take then and isn't likely to now.
I suspect that it's inevitable that Rhodey will resume the title eventually. Even the movies pointed out the inherently superior nature of the name over Iron Patriot.