WASM is going to kill spidering. We can't leave HTML if we want google to be able to read the page.
I think Google is very afraid of this. Hence their push for Angular/Polymer/AMP. If they can build a good enough platform in JS they can stall the inevitable.
In the future only marketing parts of the site will use JS/HTML. The "web app" part will be some language compiled to WASM throwing frames to the canvas