Anybody can run guix publish however and self publish their own non-free substitutes if they wanted, plus there's all the existing non-free substitute servers around, and you can try your luck with guix import from nixpkgs. The community won't help anybody if they ask for help with non-free software though.

I haven't missed any non-free packages since switching to Guix surprisingly, I always seem to find a free alternative though my daily req are pretty basic.