I can’t agree that , for Australia, it’s really ‘possible to create a dedicated area in a zoo’. The best that is possible, if species are to share the some part of their distribution, is 3 habitat species (koala, dingo and, now, platypus) in temperate eastern Australia. In all other regions, only two (or fewer) species are in-game. Central Asia and Central America / Mexico are both much better represented than any part of Oceania. IMO Australia would need (excluding flying birds) at least:
Emu
A wallaby
A wombat
to be able to make a realistic Australian zone.
To be fair, Australian regions in the rankings, should be split, as has been done for all other continents. Specifically:
Tropical North Australia: 2 habitat species
Arid Central Australia: 2 habitat species
Temperate Eastern Australia (including Tasmania): 3 habitat species
Temperate Western Australia: 1 habitat species
I thought a lot about Australia. Let's review the habitat animals:
1. Kangaroo - iconic and common around the world
2. Cassowary - exotic and relatively common
3. Saltwater crocodile - iconic and common in certain regions
4. Koala - iconic, highly specialized, and very rare in zoos
5. Platypus - iconic, highly specialized, only found in Australian zoos and SDZ
6. Dingo - somewhat derivative and uncommon in zoos, but still a famous australian animal
With 6 habitat animals, which are mostly iconic and endemic to the region, I can't say you can't build a dedicated australian area, and it's in a much better state than the middle east, Sahara or non-tropical SA, which are practically empty.
The main problem with Australia starts when you look for realism. We are missing common zoo animals which are much more 'basic' and less specialized than the one in the game. For me these would be:
1. Emu
2. Wallaby (any)
This means that no matter how many more specialized animals we get, (for example; echidna, tassie devils or tree kangaroos), without these 2 species the realism problem will remain.
So by the criteria of the list, the problem is with a few specific missing species, which puts it in the second tier.
And I don't want to split australia to sub regions, because that would require splitting much larger and climatically diverse countries into sub regions, like China and the US.
I split the regions based on a combination of climatical and cultural lines, and based on how biodiverse they are when it comes to zoo animals.