I see I had completely misunderstood what you meant. When I last used NixOS, some 3 years ago I think, I didn't really use the channels. Since I wanted to make some modifications to some files in nixpkgs, I preferred to have the nixpkgs repo locally. Seems I forgot about them.

EDIT:

> The default way to consume nixpkgs is through channels which today does not involve git. And a nixpkgs git checkout is over 1GB (my .git dir is currently sitting at 1.4GB on this machine). So that's not great.

One could also add tags to the repo in the form of pname-version for every package. I wonder how well git can handle that many tags...

In any case, the advantage of being able to do this from the git repo is that you wouldn't depend on someone forever hosting every version of a channel. I would think one would discard old channels before they discard git history.