Should there be guildlines for bounding friendship?

Except for very simple classes, C++ friendship should be more like human friendship. The secrets we divulge to each non-stranger is distinct to that particular non-stranger. We generally don't want anyone to know all of our secrets. Could there be guidelines for capturing statically-checkable limits to friendship in code? Maybe following the pattern illustrated by this example: https://godbolt.org/z/Ztw-SQ

The caveat is that bounding friendship could be a crutch that enables overly complex classes. Programmers have a tendency to not break up large classes when they should. It's a partial backslide into the "it's easier if everything's global" philosophy.