But that is under the assumption that the libraries are unbundled in the first place. And if they are, you have a choice of 'force upgrade all users when upgrading a library' or 'allow some users to stay on the older library and provide tools for the user to diagnose'. No obvious winners here, can imagine very realistic situations where one would want option A and not option B or vice versa.

The important (and OT) point seems to remain that AFAICT functional package managers do not (can not) help with the bundling problem. Still desirable of course.