Indeed can be done, proof of concept shown in this talk: https://www.youtube.com/watch?v=X8LwaDjcr7M

Regarding sandboxing - everything WebAssembly is heavily sandboxed already, and requires cross-origin isolation in the browser, so we can use SharedArrayBuffers.

So that's likely no worse than running LibreOffice containerized on a server.

Oh whoa a 5 minute video for exactly this :) Apologies for making you be my Google. Yep, everything in wasm makes things much easier to work with, especially if you want to run it on a client device