Do you expect that an updated version of, say, https://github.com/NixOS/nixpkgs/pull/36842 will not get replies like [RFC] nixpkgs/tests: create nixos-independent PoC tests by 7c6f434c · Pull Request #36842 · NixOS/nixpkgs · GitHub this time around?
Of course Automatic UID allocation by edolstra · Pull Request #3600 · NixOS/nix · GitHub or its updated version https://github.com/NixOS/nix/pull/4155 could also work for making a cheap version of NixOS tests…