I use Guix as my daily driver and do occassionally come across software that hasn't been packaged. The big ones for my work that immediately come to mind are:

- slack

- kubectl

- terraform

- azure-cli

- cscope

There have been a several other missing tools for personal use that I just ended up packaging and sharing upstream. For the ones listed above, though, I just haven't gotten around to it, so I let Nix fill in the gap, hehe. FWIW, Guix already has Nix packaged and available as a service, so having parallel stores is really straightforward.