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And I am not saying this to bash Mozilla: I think they are essential for a good Web. But that's exactly why I am concerned they are spreading themselves too thin.
For example: WebGL can run Quake2, but NaCl could easily handle Epic's "Project Sword" http://www.youtube.com/watch?v=x2ncmwgJzqw
That "Project Sword" demo is built with OpenGL ES 2.0, which is the same API WebGL is based on. All the GPU-based effects will work exactly the same in WebGL. The only part WebGL might have trouble with is the CPU-driven particle systems and cloth simulation, but even there you might be surprised at what V8, Nitro, and JaegerMonkey can achieve these days. And if the performance still doesn't satisfy you, GPGPU is now an option.
"Some ARM and x86-64 support is implemented in the source base, and we hope to make it available for application developers later this year."
The port to ARM and x86-64 are pretty much done by the way. Also, see:
Personally I suspect JavaScript (or a subset of it) will get to the speed of native code sooner than we can run native code in a cross platform way in most of our browsers.