You can have multiple WASM modules communicating with each other (though you would probably need extra interop code?), or statically link them into a single module, the concepts work mostly the same
With a browser plugin I'm sure you could swap out a WASM module on the fly, if said plugin doesn't exist, maybe it should. Would make debugging in a prod URL simpler if you can just load a page with a testing WASM file.
Is there a browser plugin enabling to swap out any parts of a website/app with own ones? With prompt/vibe-based input, so any user can customize websites in any imaginable way. Maybe it should.