People are already making games in OpenGL and C. This was totally impossible before, using JavaScript. Redesigning the whole API would delay the process, and it would have to use OpenGL as it's own backend anyway, so you'd inherit a lot of the problems.

If you want something that's easier to use, wait until game engines for JS appear. This is supposed to be low level.

With NaCL you might end up being able to use OpenCL to construct your own 3D rendering stack and use it in the browser.