Ken Watanabe should totally be a Bond villain.
I've only seen him in Batman Begins and The Last Samurai, which could have been called Dances with Samurai or Ken Watanabe Rules. I liked The Last Samurai a lot more than most people, apparently. That may make me an imperialist dog, culturally speaking, but I enjoyed it. What's not to like? It had samurai and ninja and Ken Watanabe totally steals the movie from Tom Cruise.
In The Last Samurai, Watanabe plays doomed samurai warlord Katsumoto, who has mastered the ancient Japanese art of looking like an utter bad ass. In Batman Begins, he played a convincing "R'as al Ghul" and maintained his dignity despite the facial hair he had to sport. The presence of ninja in both movies may have biased me slightly, but I think Ken Watanabe has the presence and vibe of a Bond villain.
I vote Ken Watanabe as the main villain in Bond 23. Go Ken or Go Home.