What's not bletcherous about the # @directive syntax, especially after you add some mechanism of escaping that perl the compiler knows how to ignore but doesn't also turn normal commented-out code into formatting directives?
What exactly is portable about "it runs on Linux and Windows users can just use HTML"? Do you know on how many other platforms Perl can run? You don't know how big the Texinfo distribution is, so I assume you likewise have no informed idea about the platforms it supports! How can you possibly argue that it's anywhere nearly portable enough to be part of the Perl 6 core without knowing at least these two important facts?
What exactly is easy to extend about Texinfo unless the Perl 6 maintainers fork their own version and add their own features, rather than relying on upstream to make those changes?
How exactly is making everyone who wants to write POD in Perl 6 learn a completely new style of syntax with a new escaping system that POD has never needed before not an arbitrary change?
Is Texinfo seriously an order of magnitude better than the POD 6 proposal? That's my threshold for such a large change. You have to address my four objections in a seriously impressive fashion to get my vote.