I was thinking of having merge commits. This gets hard to represent in ascii art though . Anyway let’s not go into this further since if I understand correctly you want to be able to do updates touching multiple steps in a single MR.
That was exactly my thinking. So the ‘master repo’ might have all steps side-by-side on the same commit (for example flake-step1.nix
, flake-step1.nix
, etc or step1/flake.nix
, step2/flake.nix
etc). There you can collaborate and update all steps in 1 MR.

What worries me here is how to test stuff quickly and interactively in the development repo: the flakes in the development repo should work identically (and have the same external interface including stuff like
nix run github:user/repo/branch
!) to the ‘official’ ones.
That won’t work, but perhaps that is not such a big problem: if generating the ‘visitor-facing’ representation of the flakes repo is fast then you can just run that script each time you want to test - perhaps even automatically on file changes.