GNU Guix and Nix are functional package managers.
That's fine with me, but one of the Guix/Nix people will have to contribute a backend. It's not a trivial amount of work, probably a few man-months of coding.
Filed against Nix here: https://github.com/NixOS/nix/issues/233
I also filed it against GNU Guix: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=17152
and gnome-software here: https://bugzilla.gnome.org/show_bug.cgi?id=727367
FYI, a few issues have been raised by the main Guix dev:
"It seems that PackageKit is not well suited for non-root install systems
and per-user profiles". That would probably be the first step towards making the two systems work.
Basic nix support was now merged to master https://github.com/hughsie/PackageKit/pull/126
We moved the upstream bugtracker to GitHub a long time ago. If this issue still affects you please re-create the issue here: https://github.com/hughsie/PackageKit/issues
Sorry for the impersonal message, and fingers crossed your issue no longer happens. Thanks.