I sunk a decent amount of time into WebAssembly over the past few months (I am the author of "watlings").

From my understanding, there are 3 answers here.

1. Most spaces do not need WASM. You don't necessarily see speed improvements since usually your JS and WASM (in the browser) are compiled into the same thing.

2. WASM is very good at bringing tools to new spaces. The biggest limitation here is in both tooling and education. It is not trivial to compile something like FFMPEG for the browser. Improvements to the WASI standard are helping here.

3. WASM is starting to see use in different spaces. For example, as a containerization format for efficient sandboxing.