In the changelog there were two items listed as Queen (Kitty) Hiro and Mare Hiro. What do these do and how do I unlock them? Are they art or new content?

These are skins so not really items per se. If you become Queen (loose to draw lady having beastmaster rank 3 and some check fails) or Mare (loose to centaur lady having equestrian rank 3 and some check fails) your skin (look of your character during certain animations and character menu) will change accordingly.

I do think  they should be expanded upon though. Just having it end after al l that seems kind of odd. I'd  love to  see the Queen "ending"  have a  possibility where you and your new kitty  boyfriend manage to  pull one over on the  drow and escape together to continue your adventure, same with  the Centaurs. Just have that little psuedo dating sim thing end up being more  than "And then they fucked forever abnd ever". I mean with all  the work  on how being slutty or girly  can affect how Hiro  acts  being able  to  use it  to  an actual  advantage other than making enemies  cum in combat seems like a no brainer.