Moving entirely to svg for user interface has some of its own issues (i.e. there's no default layout engine in svg; everything is essentially absolutely positioned...) but would be interesting to think about. Moving entirely to WebGL would only be viable if you don't care at all about accessibility though. For some subset of applications that might be acceptable (i.e. games), but for something like gmail or other similar applications it's definitely not.
You just have to create widgets libraries, compile them to WebAsm or something alike, and export an event-based framework for the developers to use. It can even be in another language, compiled to WebAsm.
Or, alternatively, you can just use Flash, instead of cloning it.
