I believe Guix System (or all Nix/Guix derivates) is the closest one. Otherwise I would say Yocto (not really a distro), Gentoo and all the container based distos (like openSUSE Micro).

Yeah, I meant Scheme as you’ve already figured out.

I would say that nonguix makes nonfree stuff trivial: https://gitlab.com/nonguix/nonguix

However, I do advocate that Guix introduce an official “curated” nonfree repository (like Debian). I believe that would make more good for user freedom and reproducibility. Almost no mainstream hardware works well with the libre kernel.

Nah. GNU Guix System. Or Debian + Guix.

Nix has more packages but Guix is much more well documented and coherent (anecdotal and subjective). Also nice with scheme instead of yet another DSL.