Setting aside all of the “That doesn’t seem logical” or “That’s unlikely” stuff, hit me with all your wants for DLC packs. Since we’re currently in a 5 animal (4 habitat and 1 exhibit) format, let’s keep it in that format. Otherwise, tee off.
I love all the biomes and regions, so for me they can't go wrong. But since I read this as a more creative brainstorming thread, there are two specialty packs in addition to birds that I've been thinking about, but which I haven't actually settled on a full roster for.
One would be a specialty petting zoo pack, that might come with new walkthrough mechanics (to allow the petting zoo) or new playground mechanics for guests. The key thing that I think would make this more interesting to a larger group of players, though, is if they picked some rarer breeds of standard animals to include. So for example, the highland cattle or the vietnamese pot-bellied pig or the alpine ibex instead of just a traditional cow or pig or goat. It could even be where they include animals like the Yak or the Przewalski's horse or the asian water buffalo, so that they're satisfying both the players who want a petting zoo system, while also keeping their focus on conservation for those who want to make separate habitats or incorporate them into other regions of their zoo.
I've also been thinking about some creatures that would be great for small-to-medium sized habitats. Things similar to the red panda or the pangolin or (presumably) the new caiman, whose land requirements could be fairly low and thus could be used as "filler" habitats. (Even if some of us will end up building palaces for them anyway!). If they got really ambitious, they could even develop burrowing mechanics for animals once they've mastered diving, swimming and flying. (Again, this thread said we could set aside logic or likelihood, so this is not an expectation). But I started thinking that a lot of interesting animals could be bundled under such a heading -- armadillos, badgers, squirrels, moles, platypus, wombats, prairie dogs, gophers, wolverine, tasmanian devil. At first I worried that such a pack focused on smaller burrowing animals might not be as flashy as aquatic or aviaries and therefore might not sell widely enough -- until I remembered that they could put the highly requested burrowing meerkat as the poster animal, and it would sell itself!