If someone makes this, for the love of whatever diety/dieties you defer to, don't make it do so without the user's choice to switch it off. If we want to risk full versions on 2G, let us have that option. That said, it's actually a very nice idea, to automate the switch upon hitting 2G to a mobile useragent.

Meanwhile, I think most sites are still not dickish enough to stop taking MicroB as a full browser. Facebook, I heard, and now GMail, is making us default to mobile pages, and I'm already flipping about that...