Right now we can use any language which can be compiled to JavaScript. What will change? Wasm is not faster than JS.
Webasm is not so compatible. I tried to run random demo and got error message: CompileError: wasm validation error: at offset 8: binary version 0xd does not match expected version 0x1. WTF?
I tested https://webassembly.org/demo/Tanks/ demo, and on my system (Firefox, Fedora Linux 26), asm.js version is a bit faster to load than Webasm version. (Turn off support for Webasm in about:config to test). Asm.js: 1.57s to load from cache, Wasm: 1.82s to load from cache.
So what will happen when webasm finally more closely match traditional backends?