Tonight I discovered that the Iron Man 2 trailer was released, which was a lot better than I expected, BUT... At a closer look, I think it may confirm the Mandarin's appearance, and maybe even something else...
If you pause it around 2:19, You'll get these shots:
See that Japanese-style gate behind War Machine? WHY would a movie featuring only Russian villains have a fight taking place in Eastern Asia in it? And wait, there's even more! Within that red gate, I see some vague red figure. The only things I can come up with is that we'll get to see Crimson Dynamo after all, or Fin Fang Foom is going red. Well, unless he's facing Satan or anything ;-)
If you zoom in on this one, you can also see light coming from the chest area.
Maybe I'm wrong, but I wouldn't be surprised if Whiplash isn't the final villain...