[mvindahl]

There is a tradeoff between development speed and execution speed. For web apps, development speed is usually the most important of the two and the language ironing away the most technical details tends to be a strong choice.

Roughly speaking, C is further from the metal than assembly (and WASM) for obvious reasons; Java is further from the metal than C (or Rust) due to having garbage collection, and Javascript is slightly further from the metal than Java due to abstracting away threads (the gap was far wider before Java got lambdas). LISP, of course is off the scale due to abstracting away readability ;)

On a serious note, though, I don't see the advantage that Java or Flash or Silverlight would bring to web apps unless they bring greater development speed.

But I do see WASM as an excellent future supplement to JS-based apps, for optimizing time consuming parts of the code.

[pjmlp]

It will be like Unity, Unreal do nowadays, and how many plugin runtimes used to do in the past.

The productivity of doing WPF/XAML development with RAD tools like Blend, using an export button to generate an WebAssembly executable.

I might be wrong, but that is where I see it going to.