For what it's worth, I've long since adapted to the status quo here, so I'm happy for this to just be closed :-).

(Apple seems to have mostly given up on "domains" as a user-facing or even developer-facing concept, so searching /Network seems like it is not relevant any more.  /System is now read-only even for root and they're deprecating the Python installed there; still, the up-to-date reference for the relevant API is https://developer.apple.com/documentation/foundation/nsfilemanager/1407726-urlsfordirectory?language=objc# )