Again that would be an exponential amount of work for me, and nothing more for the player than the exact same gameplay.
I guess at some point I could make a similarly looking creature for another biome, and use that as a mean to make the other sex. Like I need a female bison for a new level, so I can reskin it into a female minotaur, and reskin the current minotaur into a male bison.
Until then I'll stick to the plan and pray I can reach that point! Doing so I could complete all the NPCs while still adding new stuff to the game.
Another thing making it complicated, I'm supposed to add an attack system during the sex animations! So the player can either block or take the damages. Which mean animating that for every current sex position (player block, player hurt, NPC prepare, NPC attack).
I'd love to add it in a very intuitive way for the player, so it looks like an interactive sex act where the player try to survive the monster. I guess not all monsters would be able to attack...