Natal with a controller doesn't make sense at all, since in that case, you lack the precision and the reaction time of Sony and Nintendo motion control systems. It wouldn't make sense.
Emulating buttons wouldn't be achievable either. Stop dreaming.
As it is now, Natal is just another MS useless gimmick.
Devs everywhere are already praising Sony Motion Control for being useful and compatible with Wiimote. They're also saying they don't know how to make Natal useful...
No controller in hand means no valuable game. Sony has been explaining that for years, yet MS still tried to reinvent the wheel and failed. Again.