I must agree about Hamilton. He has changed in recent years, although I could see him heading off to Moto GP within the next few years!
doubt he'd compete in the support classes, and he wouldn't risk it I don't think. Motorbike racers will be able to compete in 4 wheel racing, but I doubt anyone in F1 would be able to be competitive in MotoGP, and vice versa, for the majority. If there was anyone today that could do both, it would be Rossi. I'm not aware how fast any of the F1 guys are on two wheels, but I'm aware Rossi is fast on 4 wheels. It's an interesting topic as I can't think of many people making the switch between the two sports.