That makes sense. My use-case simply didn't involve GUI browsing. It's pretty easy to read the 02 index file either way. What I found CPAN::Mirror::Tiny to be useful for, was in taking distribution tarballs, using them to build the required file structure and index file, which is the bare essentials of a Darkpan.
I suspect if I wanted browsability, I would probably still use CPAN::Mirror::Tiny to build my darkpan, and then use a different module as the business end of a web GUI. I don't see this module as excluding the use of a GUI-providing module. But it is entirely possible there's a more suitable alternative for your needs.
Incidentally, I actually intend to talk about building a Darkpan at the online / virtual version of the Perl Conference this year. But my talk will spend some of its time on how to convert internal use modules into distributions that are suitable for an internal darkpan, and the strategies we used for building and shipping to the mirror. I hadn't intended to get into anything regarding a front end GUI.