Yeah IMHO nix just needs someone like Brian Kernighan to sit down and write the definitive book about it and its internals. Something that clearly explains the practical and theoretical uses of nix and nixpkgs.
Nix pills, the official manual, etc. aren't really there yet--they talk about all kinds of paradigms that might (?) be going away like nix-env and its ilk. It's just extremely painful to track down the current best practice and way to do things in nix--you're bouncing off all kinds of docs and finding multiple conflicting or out of date ways to do things. Someone needs to give folks a slim book about nix flakes and the flakes way of doing things, the nix language, and a tour of nixpkgs, and IMHO there will be a lot more people using it.