The os update and backup now include etckeeper as its part of the
workflow.
The os updates now have the same name on all systems. That should reduce
friction, same command for same workflow, just different implementation.
No need for overlays.
Instead create own packages and call them via callPackage.
That will keep them simpler and allows dependency injection.
I can follow existing patterns from nixpkgs, etc.
Daniel Siepmann