They have done a 12 animal pack before with grasslands and I could easily see something like that happening again for a easy bigger final pack because its easy to just retexture the same looped exhibit animal 5 times to boost total numbers.
Also based on the information we have the only option that is impossible is fully aquatic habitat animals as there is no precedent for it. We do currently have a fully aquatic exhibit animal with the axolotl so a fish is an easy transition we have bats and butterflies so birds are doable. they are not impossible within the framework currently given just very unlikely because of future potential selling power and how they would currently have to be implemented being not optimal.
I do feel it is reasonable for us to assume that the final dlc will be bigger since most previous games of this genre released by frontier have had a bigger final pack. It probably wont be much bigger a scenery pack with 8 animals or an animal pack with between 12-20 animals is most likely and a large portion will be easy retextures. this will however likely not be this coming dlc the timing just doesnt feel right.
Getting 5 types of exhibit animals might work, if they're macaws. There would be more going on than with the butterflies of course, and I doubt it would happen, but if it were to happen, they'd be the birds I'd think it would happen with.
So maybe a Latin American pack:
Coati
Howler Monkey
Rhea
Patagonian Mara
Ocelot
American Flamingo or a second primate. Second primate should probably be the priority but I can see them going with the Flamingo instead.
Spectacled Bear
5 Macaws.
I'd gladly take the Brazilian Porcupine over several of these, but given we'd almost certainly get the Coati in a Latin American themed pack (I shudder to think of the reaction if we didn't!) as well as a primate (again, I can't imagine the reaction to a LA pack with no primate). BP seems a real stretch on time and resources. Although...time wise..maybe. Who knows. I definitely would be okay without the Ocelot, I just figure it's a shoe-in, since it's a cat, and a small sized cat for a continent that doesn't have a small sized cat