there are numerous distributions (…) for which it would be tedious and error-prone to specify each constituent dependency seperately. The existence of such distributions renders strict per-module dependency specification impractical.
Perl::PrereqScanner makes short work of that.
The only safe assumption for an author to make is that some fraction of the user base has listed the primary module of a distro as a dependency when they really want a different module within the distro.
This looks like some sort of circular argument to me: "I advocate per-distro versioning, and some people already do per-distro versioning, so per-distro versioning should be done generally."
In the majority opinion, when someone does per-distro versioning, it constitutes an accidental bug and should be fixed to become per-module.
leaving all other modules without versions
This only works if the proposal is universally accepted and implemented. (This is already implied from the later section "Recommendations", I rather want to say this explicitly, too.)