Huh, that is nuts! It’s an interesting approach, could make porting to other platforms much easier. I’d be interested to hear what the performance is like and what weird issues come up (e.g. how do you handle multi-touch, audio, data persistance, …). I guess HTML 5 helps a lot.
Are you planning to do the whole game as a WebApp or just use an embedded UIWebView for rendering in a regular app?