Yep, this is pretty much exactly what I'm looking for, thanks!

As a though experiment, how could NixOS be packaged with this for consumer users?

For stuff that's not in Nixpkgs like this, IMO flakes is the best option. Both of these require flakes.

On the topic of deploying flakes to consumer users. I'm currently exploring using https://github.com/nix-community/nixos-generators to create pre-made install iso's for a full "batteries included" experience. You can just "overwrite" the regular nixos image. Its Nix all the way down.