The "with dynamic memory" part being critical, since that means no asm.js. With asm.js, emscripten is faster.

I get the feeling this is one the one hand pretty cool, but on the other hand poorly timed. Unless WebAssembly never arrives or arrives really late, there's going to be a way to run almost-native code with dynamic memory allocation fairly soon. So it's likely this will soon be relegated to "old-android support".