That's correct.

Have you tried compiling Linux as User Mode Linux with emscripten? I imagine something like this https://github.com/nabla-containers/nabla-linux would run on wasm, too?

Well, User Mode Linux would still require an underlying Linux ABI, for example mmap to implement pagination. With sufficient work it might be possible to actually run UM Linux _on top_ of CheerpX / WebVM.

Implementing the Linux ABI ourselves gives us the opportunity of a tighter integration with the Web platform anyway.