Too late, WebAssembly is already here.

I really think it will bring Flash like web sites back, and browser vendors are the ones actually pushing it.

The wheels are already in motion, with everyone trying to port their favorite language or VM into WebAssembly.

For example, today it is Qt WebGL Streaming, tomorrow it might just run directly from WebAssembly.

http://blog.qt.io/blog/2017/07/07/qt-webgl-streaming-merged/

It will be up to those frameworks to provide usability support, like WPF does for Windows.