It would also be (academically) interesting to extract pkgs/pkgs-lib and it’s secret twin the pkgs/build-support, conceptually they are on the same layer of packages dependent library functions. They could well go into the same conceptual bucket as builtins.
Can anyone enlighten me about the associated costs of providing pkgs dependent library function with different pkgs version than the (potentially the same) packages they actually would build? (besides the obvious downside of increased closure size).