The other comment already answers part of it, there is no real need for it for a NixOS system as you usually either can consult the store on the machine (and recursively build a graph of a all transitive dependencies of a generation), have a system that stores the config along with the generation (option `system.copySystemConfiguration` or a flake-based system will store the config in the store itself).

A system that has neither a store nor the config (container image) not easily reconstructable as you miss too much metadata.