I'm playing with Guix and even made a dedicated installation. I find it more attractive than Nix (more sane language, shepherd service manager), but it lacks in diversity of packages and many of the ones I require are very stale.
Patches are welcome :)
Not all patches are welcome. Guix is very strict and opinionated - they won't allow unfree packages or firmware updates.
I was told you don't need to subscribe to the mailing list, but I've sent mailing list messages with patches, discussions on technical issues that were never accepted.