Something like the (long forgotten) official animal editor that Zoo Tycoon 1 had, to let people create their own animals. Obviously, it would be waaaaay more complicated than it was back in ZT1 days. But an officially released framework that would let creators design new kinds of real-world animals and put them on the Steam workshop would be really interesting. This could conflict with potential DLC animals however, so perhaps it would be released late in the game's lifecycle. I would just love a modding community similar to the one out there for the Zoo Tycoon series. Thoughts?