The more I've thought about it, the more the idea of Ghost being a villain in Iron Man 3
appeals to me.
I think that Ghost is a particularly strong Iron Man villain, because while a lot of the Cold War themed baddies have aged, the Ghost feels more relevant now than ever, and is literally more prominent in the comics than he's ever been. The idea of an industrial sabateur with an obsessive hatred of big business and multi-national corporations is something that I think could connect with today's moviegoers and really make for a compelling antagonist to the Tony Stark of the movies. I think there's also enough scope in the character's rampant paranoia to attract a good actor to play the role.
And on the technical side of things, Ghost manages to raise the stakes, I think. He has a suit that's more technologically-advanced than Stark's - allowing him to turn invisible or to phase through walls - but at the same time it is radically different from the Iron Man suit or the Iron Monger "bigger and badder" school of thought. As a result, the recurring theme of "technology in the wrong hands" among the villains is maintained, but they're also helping to avoid the films falling into a repetitive "two guys in metal suits clobbering each other" pattern.