How about Tony Jaa?

I think Tony Jaa would make a great Kato. Jet Li could look great as Kato, he's the right size & build for the job, but as far as convincing fighting skills (withouit wires or doubles) are concerned he can't compare to Tony. Then again, with Kato's mask & cap Jet could be doubled half the time & no one would notice.
As for Jackie Chan, well, I'll always be a fan (no matter how lame his movies become, he made some great ones when he was younger, closer to his physical peak) but I'd agree he's way too old for the role of Kato now. I think he should give up action movies altogether because he can't possibly live up to his younger, legendary self (watching his action sequences now is kind of sad, like watching Ali, or Sugar Ray Leonard, or Holyfield fighting long after they should've retired).
I'd also like to see a "Green Hornet" movie set in the 1940s, somewhere around that era, with Al Capone type gangsters as the baddies; I just can't see the Green Hornet & his faithful asian chauffer fighting crime in our time, neither politically correct nor remotely believeable.