Literally anything that isn't a mammal or bird! So far there's... Frog, alligator, and octopus... I would love to see turtles, I don't care if Tortimer is a thing. Isabelle is a dog and yet we have dog villagers.
Speaking of dogs, I wish the dog models were more varied than just the one floppy-eared version we have. So many different kinds of dogs and only one dog model.
Anyway, back to non-mammals, I think there should also be a "lizard" villager whose model shape could encompass lizards, newts, and geckos.
I like the aforementioned prospect of bug/spider villagers, but I don't think they would make that attempt.
I'm not sure how they could even do it but I'd love to see snail/slug villagers. They'd be so cute with their little eyestalks and whatnot.
Well thanks, now I wanna draw these ideas.