Looking at some of the top animals on the wishlist, you have things like the Wolverine, Tassie Devil, Baboon, Spectacled Bear, Tree Kangaroo, Coati, etc. The Secretary Bird I believe is in the top 3 of the wishlist and is a very wanted animal by the community, gaining even more attention after...
Aside from the very obvious DLC with aviaries, I'd personally love an European pack, with things like the red fox, wild boar and badger, red deer, European fallow deer.
I'd also like an pack with just critically endangered animals in it, like the: Axolotl, Addax, Bavarian pine vole, Dama...