Koalas are bigger than ring-tailed lemurs.
I agree, the platypus is too small to be a habitat animal. If they include a monotreme, I'd advocate for the short-beaked echidna instead.
Looking at the way they did the Arctic DLC, though, I suspect we'd see the perentie or lace monitor, the freshwater crocodile, and the dingo. Why? They're easy, and their inclusion would mean that the pack can be released much more quickly. They wouldn't get away with not including a kangaroo (I would prefer the eastern grey as a walkthrough exhibit animal, but I don't doubt it will be the red), and I'd seriously hope they would finally put an emu into a zoo game.
In terms of habitat animals, my list based on expectations as much as wants would be thus;
- Red kangaroo.
- Dingo.
- Freshwater crocodile.
- Emu.
- Short-beaked echidna.
I would love to see them somehow include the koala, but I think they might put that in the "too hard" pile. Another animal I think would suit the game perfectly is the Tasmanian devil - they're under threat from a type of facial cancer and breeding efforts have been ramped up significantly all over Oceania, so I would hope Frontier would consider the devil for Planet Zoo given the angle of "education/conservation".
Australia/Oceania would also be a good way to add more education boards; invasive species, disease, and forest fires are three big issues the native fauna of Australia and New Zealand has to face.
In terms of exhibit animals, where do you even start?
- Taipan.
- Frill-necked lizard.
- Thorny devil.
- Bearded dragon.
- Blue-tongued skink.
- Shingleback lizard.
- Social huntsman spider.
- Goliath stick insect.
- Golden bell frog.
And that's just Australia. If we included New Zealand, there are dozens more possible additions, including of course the Tuatara.
That said, I would really like to see some kind of aviary system implemented before they tackle Australia/Oceania, since a lot of the more iconic species from this region are birds. Whether they go down the likeliest route and make the PZ aviaries similar to the one in JWE, or do something else entirely, I don't think you can do Oceania justice without including a few key parrots (and others, such as the kereru/NZ wood pigeon, or the laughing kookaburra).