I think we'll either get Australia, Oceania or Deserts as the next DLC, and it shouldn't be too far away (announced in the next couple of weeks and released a week later). I'm hoping for Australia, although i think that a couple of aspects of this will be difficult to implement in a satisfying way, mostly to do with macropods (kangaroos etc.):
1: Hopping: It's hard to get the animation for hopping right - macropods move like nothing else in the game and animations of them often fail to get it looking good.... They tend to look like they're jumping from one spot to another, rather than bouncing (using the ligaments in their legs as springs). I really hope that, when they're added, the animations look good.
2: Pouches: It just wouldn't be right if joeys didn't use pouches - unfortunately, i suspect that this won't be a feature, given that birds etc. don't lay eggs in the game and the animations / behavioural programming might be tricky to implement.
That being said, i still think Australia DLC is most likely. So far DLCs have had 4 habitat animals, so i guess that's the most likely number. The SA DLC was careful to add animals from a mix of biomes, so i suspect this one will do something similar:
My prediction (not necessarily what i'd most like) is:
1: Red Kangaroo (Desert);
2: Wombat (Grassland);
3: Tasmanian Devil (Grassland) or Tasmanian (Bennet's) Wallaby (Grassland, walk-through),
4: Emu (Desert/Grassland), Cassowary (Tropical) or Perentie (Desert)
I think there is a small possibility of an additional animal.. If so I'd guess another macropod, probably a wallaby. I know a lot of people are thinking koalas are a pretty sure bet, but i'm predicting/hoping that its not there. Why? Because koala behaviour pretty much consists of sitting in a tree asleep and occasionally waking up to nibble something - Given that the arboreal animals in the game already don't spend enough time in the trees, i don't think koalas would either, and koalas spending most of their time running around on the ground just wouldn't be right (which is why i was fine with no sloths for SA DLC)
We might not get an exhibit animal (although there are lots of possibilities, there are already a reasonable number of Australian exhibit animals in the game). I also think that we won't get as many build pieces as we did for SA DLC - probably some Aboriginal themed rocks (cave paintings) and similar... However, I think we'll get quite a lot of plants (i certainly hope so!) - at least 2 eucalypts (fairly generic ones), kangaroo paw, and some other stuff.
I do think, however, that we'll get at least one new scenario, possibly a couple (personally i'd prefer more build stuff or an exhibit animal, but this is my prediction).
As a last, out there, prediction, I'm guessing a bit of a surprise: A new, Australian (red) desert map (with rocks to match) that is loaded if you choose Australia Desert as the biome.
On the other hand, Frontier has been pretty good at adding unexpected animals as well as more obvious ones so far, so who knows?