That’s basically using a different language as shell now. Honestly, I’d love for Hurd to break this particular POSIX compatibility and stick with Guile, so that there would be uniformity across the entire platform.
Or how about es (extensible shell)? It is functional, it will respect POSIX and also, it can possibly substitute Guile and Nix? I wish I had the technical know-how and patience to experiment with this, but hey, Scheme is also pretty good.