[Bahamut]

Even when it's out and mature, there is some complexity around gracefully degrading when it is not available - it is going to increase frontend complexity dramatically I suspect, at least until browser support dictates that graceful fallback isn't necessary for the feature.

[callahad]

Most current WebAssembly compilation paths produce asm.js as an intermediate artifact. In the near term, backwards compatibility should be relatively simple: save both and load the asm.js code as a fallback.

[mrec]

Or you can do it on the client side by hooking into the module loader and decompiling the wasm back into asm.js. See for example the

https://github.com/lukewagner/polyfill-prototype-1

PoC mentioned in the wasm FAQ.