I kind of wonder how David Tennant would be as a hypothetical George (not that it'd ever happen)... vocally, he's very much like Elaine Stritch, or even "the thinking man's Pierce Brosnan." He sings with great snarling intensity and passion but very little melodic quality, but he's great at brief little tuneful snatches that don't need much sustain, and falling in and out of sprechstimme smoothly. You'd need a role with lots of character and an odd vocal range with as much sprechstimme as standard tonal singing, and George is kind of that.
My guess is that if he ever did it, it'd be one of those performances where if you saw it, you're blown away, but it doesn't at all translate to a cast recording, and people would argue him as a best/worst George for fifty years to come.