Hey!
I think it would be awesome if SFML was ported to work on NaCl. Google's Native Client technology. This is a framework that makes it possible to compile and run native C/C++ code directy as an applicaton in the browser, with openGL ES 2.0 rendering. The only browser that supports it as of now is chrome, however they aim to have more browsers implementing it.
It handles window creation, getting an openGL context and events (key, mouse, gamepad) so I suppose one would have to make a bridge between their API that provides such (the pepper API) and SFML as well as have SFML use openGL ES. The rest shouldn't need much work.
As I have myself worked a bit with NaCl I'd gladly aid the porting procedure should it be decided to be done. I suppose it would have to wait for the openGL ES porting too.
But I strongly suggest that this is considered since it would mean that applications written in sfml could with a very little effort be deployed over the web as applications. Google has shown a quake port to native client and they claim the performance loss is only about 5%-10%.
What do you think?