Developer Brandon Jones has, after some tinkering and hard work, managed to import a map from online shooter Team Fortress 2 into WebGL. It's not playable, but it's there.
This means that in practical terms it's largely useless, but think big for a second, OK? This is one guy, working on this unofficially. You put a team of guys working on this, and give them time and money, and they just might be able to do more.
Which team? Oh, I don't know. Valve recently made Team Fortress 2 free-to-play. Seems the only place left to go after that is to get the thing running in a browser. And if Unreal Engine 3 can do it, Team Fortress 2 can do it.
You can see a vid of the map in action above. Note that, according to Jones, the sluggish frame rate is a result of his capture software; he says performance is "smooth" in the flesh.