Game development for the iPhone (and other mobile devices) using HTML5?

Is this a possibility? I have read a few articles that say the iPhone browser does support HTML5. I know small simple games are possible, but I was wondering if it would be possible to create a** large** HTML5 game, much like the Flash games on Kongregate (possibly 15-20 mb or more worth of data). Would it actually play smoothly on a mobile device and is this even possible?

I know that Flash is losing support for mobile devices so I’m looking for an alternative. I was looking at Objective-C but I would rather make my game in HTML5 if that is a possibility since it will have more support in the future for mobile devices and would also work across multiple devices.