He kind of was out for revenge. That's why they showed the stuff at the beginning. It wasn't his sole purpose, but he did want some revenge.
I'm glad they went down the route of different, being that the villain WASNT a guy in a similar suit. However, I would've gone ahead and done Mandarin with the alien tech rings... The big hold up before was that they wanted to keep Iron Man grounded and stay away from the alien stuff. Well, you opened that can in Avengers. You showed alien tech can work in MCU. Go with it. Don't take Iron Man's most well-known villain and turn him into a fake.
I would've had something like Mandarin runs the Ten Rings, hires AIM to create Extremis so he can have a small group of super soldier terrorists. Killian takes it as well, becomes what he was in the film, just be the side villain. Tony would have a whole new set of problems he's never experienced... He would have to learn something new to defeat an alien tech he doesn't understand. Challenge his mind as well as his body. Iron Man has an epic battle with Mandarin while Iron Patriot and maybe the rest of his armors controlled by JARVIS as they were here fighting the soldier and Killian.
I haven't thought out the details, but I think it could've worked.