Ben Kingsley is The Mandarin!
Maybe it's a bit early to discuss the possibility of the Mandarin being the villain this time round. I just think it may be a case of 'now or never'. I think with the Ten Rings in IM1 and the interviews with the actor who played that group's leader has implied that they were intending to do the Mandarin at some point. Couple that with IM3 possibly being RDJ's last Iron Man film I think this is the best time to go with the guy many believe to be Iron Man's nemesis.
I just think it would be a real shame if they miss this opportunity. Even if they made the Mandarin a villain in the Avengers sequel it would likely rob Iron Man of a great story between him and the Mandarin, which in his own film would be able to focus more on them than trying to give as much motivation to all the Avengers.
Also, I'm curious to who people would want to play him in the film. I'm torn between either having the Ten Rings leader become the Mandarin which if done right could make for a powerful story or having him return as a henchmen to the Mandarin (played by someone new).