If Perl6 were to use an existing doc standard from which to base it's Pod, it would make sense to me that an implementation of this existing standard would simply be listed as a prerequisite, rather than actually being distributed along with Perl6 proper.
Well, the distro has to include internaldoc-to-man at a minimum, or Unix admins around the world will scream. And I don't even think a texinfo-to-man exists, because texinfo is too rich to fit into manpages. In fact, that's the problem with your proposal as well. According to texinfo
Notable is the lack of man as an output format. Texinfo is used to write the documentation of GNU software, which typically is used in Unix-like environments such as Linux, where the traditional format for documentation is man. Man pages have a strict conventional format, whereas typical Texinfo applications are for tutorials and reference manuals. As such there is no benefit in using Texinfo for man pages, which are traditionally quick reference guides. However, many GNU projects eschew man pages nearly altogether, referring the reader of the provided, and often self-describedly seldomly maintained, man page to the Info document