Iirc they have talked about adding variants of animals but want to do it in a good way. Instead of just slapping different textures on. You can get away with that for tames since most people don’t own chickens, cows, pigs, etc as pets. But plenty do for cats and dogs. So maybe having biome specific animals comes with certain traits similar to the bogged, stray, husk, etc
There are all sorts of things they could’ve added to the game while leaving a base version untouched. “Minecraft vanilla” is what that’s called right now, but only because modders have actually been doing the work. Minecraft devs have barely contributed a game’s worth of content in the 13 years since release. They’re gonna get outflanked by games like enshrouded due to their own negligence.
I do too lol. I’m just saying the general population. Plus they’re similar to hostile mobs where they provide a service (in this case egg production and meat) so having a slight difference between chicken varieties would probably happen. Zombie, husk, drowned, and the same for other mobs