Have you tried using something like `home-manager` (https://github.com/rycee/home-manager)? It gives you declarative package and configuration management with Nix on non-NixOS. It might be a nice compromise until NixOS/Nixpkgs is mature enough to meet your needs more completely. Or maybe you'll never switch, if you really like the convenience of being able to easily grab a trendy package from AUR or whatever. But either way, there's a lot of declarative Nix-y goodness you can get on Arch Linux! :-D

There's a similar tool for macOS called `nix-darwin`, as well: https://github.com/LnL7/nix-darwin