I recently tried to make a Furry Fortress mod that would let you play as various animal-folk. Unsurprisingly, the framework of Dwarf Fortress was ill-suited to the task. I want to share my list of things I wanted to do but couldn't.
Civ-Specific Livestock and Crops: Would have liked to do fun things like lizard-folk with crocodile mounts, ant-folk with giant aphids, panda-folk with various flavors of bamboo or carnivores that can grow textiles but not food crops.
Obligate Herbivores: There's a carnivore tag but no herbivore tag, which means I can't stop rabbit-folk or horse-folk from being able to hunt or butcher, even though their civs consider this behavior unethical.
Milk Tolerance: When designing lizard-folk and bird-folk, I would have liked the ability to make them unable to tolerate milk-products and disable the Milk Animal/Make Cheese jobs.
Non-Clothed: Creatures like ant-folk or lizard-folk should care less about what they are wearing. It is also weird to see duck-folk or centaurine-horse-folk demand to wear socks and shoes.
Alternate Addictive Substances: It would be interesting to expand ALCOHOL_DEPENDENT to work with other substances, like meat, tea, honey, fish, bamboo, carrots, cannabis, or whatever.
Marriage Style: Not all animals (or for that matter people) prefer life-long monogamy. A plethora of possibilities present themselves, especially in the context of animal-people. At the simplest level, MARRYING or NONMARRYING could be used to distinguish between races that don't form bonds when they hook up. Could be creature level or civ level token.
Graphical Caste: Would have liked to do things like making a lions, leopards, tigers as castes of a larger panthera-folk, but that change would have been purely cosmetic and there's no way to portray that cosmetic change graphically.
Custom Appearance: You can't really have curly hair or long lobes if you're a lizard-folk.
Water-pathing: Having a natural ability to swim is useless if the AI doesn't realize it can.
Metamorphosis: Instead of simply going from small to large, some animals could change considerably as they grow older, such as an ant that goes from larva to pupa to adult, or a bird-folk could be born without the ability to fly and gain it as an adult. I'm sure someone would use this to make pokemon.