Well ... my aim was to write multi-file hypertext which renders well on disk, metacpan and github.

Your solution will link from local or github to metacpan.

My imagined solution would be a distribution relative path inside L<>

I thought I saw this already in the past, i.e. Module PODs linking to other internal pages generated from POD (expample, tutorial, tests, ...)

Maybe this could be fixed by introducing a new scheme, something like dist: or relative: ?