Could you articulate why? I have only been using Nix for ~3 months, but so far I do not really have qualms with the Nix language. Maybe it is because I have written a fair bit of Haskell before.

(Of course, I understand the argument that it would have been more comfortable if an existing language like Scheme was used.)

My biggest concern for Guix is that they will restrict the available packages by being overly zealous a bout package-licensing (like everything the FSF does).

Same here. When I got interested in NixOS/GuixSD I seriously considered using GuixSD, because Scheme is more familiar. But there are just some proprietary packages that I need for work (Skype) and at home. I didn't really feel like having to rely on third-party repositories, etc.