Do you have any reference for that? You can already technically use whatever you want and wasm will not remove the need for high level languages also having to supply a (multi megabyte) runtime as there is no direct mapping to wasm instructions unlike with C++ or C.
Eich's comments on HN and on Twitter. It was all discussed when wasm was first announced a while back. I'd dig up the exact source comments from Eich, but at work. You'll probably see enough comments from the wasm folks in this post to verify whatever particular technical specs you're interested in to satisfaction.
