I think it's a bit of both, and maybe more. For one thing, I think there are historical ties to asm.js (i.e., some of the same people went on to develop WASM),

I think it's a bit of both, and maybe more. For one thing, I think there are historical ties to asm.js (i.e., some of the same people went on to develop WASM), and asm.js should compile nicely to WASM. Once they have GC figured out. For another thing, I think there is the long-term goal of using WASM as a way to migrate away from JavaScript, if desired. Once you can compile all (or most) of your JavaScript logic to WASM, you can start transparently replacing parts of that code with code written in other languages that compile to WASM. If the interfaces remain unchanged, the remaining JavaScript won't notice.