In a sense, nixpkgs is that. And AIUI that's exactly that the author refers to by "95% is nixpkgs". The NixOS part (the module system and modules) is in no sm

In a sense, nixpkgs is that. And AIUI that's exactly that the author refers to by "95% is nixpkgs". The NixOS part (the module system and modules) is in no small part integration between the init-agnostic nixpkgs and the init system (systemd). That's what enables this project, as well as nix-darwin (integrates with launchd) and NixBSD. The traditional way (pacman, apk, apt...) is for packages to carry the init files for the service they package.