I think "native" web-tech like JavaScript & HTML will still have a lot of momentum in it. WASM is about other languages getting access to browser as a delivery platform. I wonder if language JavaScript that was originally designed to run on the web should have a competitive edge here?

The drawback of JavaScript has so far been its low execution speed, maybe WASM will make it run faster.

In other words maybe WASM will not be the downfall of JavaScript but its uplift.