What Nix and build tools need to agree on is a specification or protocol for "building a software dependency tree". Like, I should be able to say 'builder = cargo' in a Nix derivation and Cargo should be able to pick up everything it needs from the build environment. Alas, there is simply far too much tied up in nixpkg's stdenv for this to be viable, so we have magic stdenv builder behavior via hooks when a build tool is included in nativeBuildInputs.