an OS based on WASM could have merit
Came here to say this. Beyond Rust and AssemblyScript, there are quite a few other programming languages that target WASM, meaning that WASM is a good candidate for that holy grail, the unified environment where you can write your stuff in 'any' language and re-use and talk to stuff written in 'any' language without relying on relatively clunky, type-challenged and slow IPC.