Right now nixpkgs doesn't expose everything that is used internally in its flake. This defines a flake with more of the internal modules exposed.
In particular, it includes installer profiles and image building modules.
Git repositories for the sub-flakes can be used as separate repos:
These are maintained using git's subtree functionality because submodules do not currently interact well with nix flakes.
Most modules are slightly modified in order to include an enable option which defaults to false.
I'm not too interested in maintaining this repo for the long term. If others do find this useful, I would suggest we contribute back to mainline nixpkgs or otherwise I'd also welcome transferring ownership to nix-community.