The Hughes Brothers are going to be directing the movie version of 'Kung Fu'. If they're smart, and based on movies they've made in the past I know that they must be, they'll hire David Carradine to play either Master Kan or Master Po. Or have him involved in some other small cameo role.
This would be a sign that the movie has received the blessings of the star of the TV show, which goes a long way toward fostering good will in the prospective audience.
Best example of all? Ben Stiller and Owen Wilson as 'Starsky & Hutch' who meet the original playuhs at the end of the film - Paul Michael Glaser and David Soul. It was a cute moment which topped off an already pleasurable experience of a buddy movie.
It doesn't guarantee that the movie will be any good, of course - consider the movie version of 'The Avengers'. Even with the participation of Patrick Macnee (in voice only) as Invisible Jones, having the original John Steed couldn't translate to the entire affair as being a good movie.
Roger Moore supplied his vocals at the very end of Val Kilmer's version of 'The Saint' in a radio broadcast. By that point, it didn't matter; the movie had to stand on its own merits. (And it wasn't bad, considering it had become basically a generic "blowed-up-real-gooder" that wasn't much different from movies made by various action stars over the previous decade.)
But at the very least, if you do make the offer for the original TV star to appear in the cinematic remake, for God's sake, make sure they accept. I think the refusal of Robert Conrad to take on a cameo role in the remake of 'The Wild, Wild West' helped begin the antagonistic feelings towards the movie which starred Will Smith in Conrad's role of James West. (I think Conrad was offered the role of Ulysses S. Grant, but I can't be sure of that.)
The fact that the movie just plain sucked because it had to bend over backwards to create a logic for Smith's West to be in his line of work did the rest.
But should the Hughes Brothers offer any role to David Carradine, it should at least not be as a villain. Although he plays one well (just check out "Kill Bill II" for proof.), the audience might see it as Carradine's statement against the movie in general.