One idea I had was to leverage nix channels to use Nix as the package manager _only for language packages_. Instead of downloading the default set of packages, you subscribe to the "Wren" (;-)) channel with `$ nix-channel --add http://github.com/wren/nixpkgs` and now you have all the local packages for your language. It could basically "be" the PyPI or RubyGems for a language.