That looks kinda cool, that it's mountable as a Redcarpet renderer
One feature I would love to see in RubyGems is man pages for gems, because man pages are underused and I can't go and look Github documentation up quickly as I have to break out of my dev box and go and open Chrome and look it up there
I would still use https://github.com/rtomayko/ronn, simply for the pretty HTML pages though