Very interesting question! I like the idea of ferrets as well as chinchilla/possum, platypus and reptiles!
A lot of the species we don't have as villagers are used on special characters to make them more unique though, like Gracie the Giraffe, Kicks the Skunk etc. would be cool to see more of those species, especially an axolotl or turtle villager!
this is kind of a big request bc it'd make the programmers have to do an entirely new mechanic, but i love the idea of dolphin / shark / seahorse / other aquatic villagers! we already have the octopi, but they move around on land?? i think with these aquatic villagers, they would plot their houses in the ocean! and the human characters would automatically get a wetsuit (and have it easily equippable / not taking up an inventory space all the time) so they can swim to visit their water-dwelling villagers!
this is different from a villager-species idea, but going kind of along w the houses in water idea, i'd love it in future animal crossing games if we could put plants in water like lily pads and pretty looking floating algae and hyacinths :')
adding bats is such a good idea! i didn't even think of that. :>
i want more owls in the game, in addition to blathers and celeste. and maybe some other birds? the penguins are already super cute, but how about like... puffins? am i the only one who'd be thrilled to have grumpy and peppy puffins in my town? :x
Dolphins! Like Wendell, they can just walk on their tail fins. It'd be pretty cool! And maybe make them like Octopi where there aren't that many of them in-game.
I think Raccoons (both small and large) and Foxes should have villager counterparts. Especially Foxes, I mean, look at how cute they can be:
I'd also like to see Otter villagers as well as Kittens. There's already a Kitten in the series which is Katie so it would be nice to see Kitten villagers.
Foxes and all the aquatic animals would be really cool~
And the aquatic ones could stand on their tailfins too, though I don't know how well that could be programmed sadly </3
Maybe someday, if we're lucky-- we'll see these animals in a new Animal Crossing game~ Hopefully for the switch