What does silverblue give you on top of what Guix and Nix already provide?
In theory something like it could be a giant escape hatch so that if you run into Guix packaging difficulties for some software that, e.g., tries to fetch from the internet at runtime, you can just build with autoconf and make or `npm build` or whatever against the Fedora base system. Silverblue might be quirky enough that it has its own hiccups though, idk.
Maybe there are docs on repurposing that as a general packaging escape hatch, which someone more familiar with nonguix could point to in a reply.
Apparently there is an rpm-ostree-friendly RPM build of Nix that can be used to install Nix on Silverblue as well: https://github.com/nix-community/nix-installers/pull/8
It includes some code to get around the group/user management quirks that some other commenters have noted b0rked the Guix installer with Silverblue, so perhaps it gives an outline of how to install Guix on Silverblue for a hacker who'd like to try it :)
So doing a guix shell --container --emulate-fhs <packages> will have you in a container with the usual /lib, /bin, and so on, which should work just as a "typical" Linux distro. You'll want to share things from the host to the container (e.g. graphics) but that is all standard guix container options.
Either way, that's pretty exciting and I hope it can be merged soon!
I could install Guix on top of something like Ubuntu or Fedora workstation for the same effect, but then I'll have two system package managers side by side, which is pointless and probably error prone.