The first PR is merged 
: nixos-rebuild-ng: init by thiagokokada 路 Pull Request #354029 路 NixOS/nixpkgs 路 GitHub.
Inviting people to test once this hit the unstable branches. It should be as easy as adding environment.systemPackages = [ pkgs.nixos-rebuild-ng ]; to your configuration. Please also read the README before starting.
It would be nice to have both Flake and classic Nix users as testers, especially the later because I have no system using classic Nix.
I am also starting to work in the second PR: nixos-rebuild-ng: improvements by thiagokokada 路 Pull Request #356468 路 NixOS/nixpkgs 路 GitHub. My objective here is to implement the remaining missing features, especially the --target-host and --build-host and the _NIXOS_REBUILD_EXEC. After finishing those 2 features I think all features will be implemented and it will be mostly figuring out how to test this and rollout for users gradually.
It would be nice to have this ready as a opt-in for 25.05 and having this as the default for 25.11, targeting a removal of nixos-rebuild in 26.05, but let鈥檚 see.