Bats, foxes, bugs. Like no really, could you imagine a butterfly or spider villager? Ok, maybe not spider. But butterfly or ladybug would be adorable. Raccoons and possums (opossums? I can't tell the two apart) and roadrunners would be cool too. Also, more aquatic villagers. Whales and dolphins and squid. Mythical creatures would be cool too, pegasus, unicorns, alicorns, dragons, maybe a gorgon.
For cameo villagers octopus or squid would be awesome for a blooper (SMB series) and octorok (TLZ series).
My top 3 most wanted would be alicorn, whale and bat. There's just so many possibilities and I get excited. Like maybe dinosaur villagers.