Mechanisms similar to the here proposed providable have been mentioned in context of the std refactoring. There where mentioned ideas of some think like a header for a crates interface (possible automatic generated), creates with “parameters” allowing part of them to be specified out side and the singular (module?) interfaces I mentioned (kind of a more general approach to your pre-RFC).
All of them have in common that they want to help with situations of dependency inversion, like this pre-RFC