Here's an interesting fact: as of right now, the roster for Planet Zoo's base game is the same as the full base roster for animals in Zoo Tycoon 2. Over thirty base animals have been confirmed not counting terrarium species and counting, which begs the question: what animals do you guys wish would still be included in the game?
I think likely animals that aren't revealed yet are:
Kangaroos - We need at least one animal from Oceania, and red or grey kangaroos are the most frequent choice in zoo management games.
Penguins - It was revealed that there would be Antarctic animals in the game, and penguins are the only ones that could fit that criteria (I don't think they'll include seals or sea lions yet). We could even get one of more species like in penguin houses in real-live (king, gentoo, and rockhopper)
Polar Bears - Another continent choice was polar, and with it's strong conservation focus in zoos these days and its obvious namesake, the polar bear would be a no-brainier.
Giant Panda - I thought that the panda would've been out only or first revealed Asian bear species, but it's still a high contender for obvious reasons.
Red Panda - These are a stable in zoos all over the globe now and would be perfect for wherever you build your zoo.
Black/White Rhinoceros - I thought that these would be revealed before the Indian! It's a toss up on which may be present as the white is bigger and far more common both in zoos and in the wild, but the black rhino has been the rhino species in the first two ZT games and is rarer so it's a tossup.
Bison - The American bison is one of the biggest conservation success stories, and it would be unexpected for it to not make it. Besides, we need them to go with the pronghorn.
Gorillas - This is another no-brainier, the only bugger is if Frontier decides to go with Western or Eastern gorillas.
Otters - One of the more controversial choices but with both species of hippos and two crocodilian species confirmed, I think it's safe to say that otters may make it into the game as it's another animal to utilize freshwater. My preference is the Asian small-clawed or giant otter.
Gibbons - We need more primates and one of the most popular choices to pick from, and one that could possess some unique animations are gibbons. Lar, white-cheeked, or siamangs would go great in the game, and we could mix them with the orangutans.
Jaguars/Leopards - These two are perhaps the most likely choice for a 5th cat species in the game; I think we could get a rarer leopard subspecies like Persian, Javan, or Amur, and the inclusion of a south american tapir species makes jaguars a greater possibility.
Meerkats - This one is perhaps a 50/50; meerkats are small enough where their inclusion is unlikely, but they're extremely popular and with the confirmation of burrowing animals like aardvarks, it's still a possibility.
Giant Anteaters - With the aforementioned inclusion of the Baird's tapir, South American animals just got a lot more likely to appear, and what better choice than one of the weirdest of them all?
Capybara - They can be mixed with the tapirs, and even appear in walk-through exhibits.