Now that i think, something like a Aquatic life would be the best thing to see in the game. Now considering the possible species and oportunities with a pack like this would be so big. I always thinked that aviaries should come first, because they are too iconical to not include them, but i have been today in Oceanográfic Valencia, and i can say that marine and river animals are very awesome, specially the belugas, possibly the only cetacean that can come in the game. If one day a pack like this is announced everyone would be very surprised... "Aquatic Life Expansion Pack"... that sounds very incredible. For my case i would select a variety of fishes and various animals from freshwater, cold and warm waters, always counting with their possibilities, but maybye this is the less possible pack because of it complex animals. But here my personal selection:
Beluga: Maybye the only cetacean that can really be coming to the game. Too iconical to leave it from the game
Walrus: The last Pinniped representation, and a very requested one
West Indian Manatee: Very beautiful species and very unique for every aquariums
Green Sea Turtle: A classic one, the first marine reptile of the game
Sea Otter: Zoo tycoon 2 nostalgia, and a must for the otters family
SALTWATER FISHES
Here is impossible to guess which fishes can come, but some Sharks like hammerheads and bulls, rays like the cownose and a variety of coral fishes
FRESHWATER FISHES
Here happens the same with saltwater, but a must for me would be the arapaima. Some african cichlids and various freshwater and swamp fishes would do a very excellent selection