My primary interest in Rust is for gamedev, as an alternative to C++. The library ecosystem is a bit weak right now, although there's a lot of interest and people working to fix that, and I think the fundamental language is a great fit.

WASM lets me reuse the same codebase to host demos/previews/simpler games directly inside of a website, without needing to convince the user it's trustworthy and worth their time to download/install/grant permissions to first.

I'm sure other SPAs could also see benefits...