I figured I would go through this again - I have substituted some of my older choices and also added the Europe, Wetlands and Conservation packs.
Deluxe: Bar headed goose (one of my most-wanted species, which could be kept in all sorts of enclosures and be an ideal 'starter' species for a smaller zoo)
Arctic: Wolverine (probably one of the most obvious missing arctic mammals at this point, which could represent Asia, Europe and North America)
South America: Chacoan peccary (an endangered pig-like ungulate that would represent the dry forests and deserts of South America)
Australia: Parma wallaby (a small woodland-dwelling wallaby that lives alone or in small groups; as opposite as possible to the red kangaroo currently in the game)
Aquatic: Giant Asian pond turtle (a large and critically endangered freshwater turtle that is able to be kept in large outdoor enclosures and mixed-species displays)
Southeast Asia: Prevost's squirrel (a colourful tree squirrel that is commonly kept in zoos and suitable for keeping both outdoors and in walkthrough enclosures)
Africa: Red river hog (one of the most visually interesting African hoofed mammals that would be an ideal representative of the rainforest habitat)
North America: Ocellated turkey (a brightly-coloured ground bird that could represent the tropical woodlands of Mexico)
Europe: European rabbit (a charismatic and endangered small mammal that could be kept in all sorts of different areas of a zoo)
Wetlands: Lac Alaotra gentle lemur (a critically endangered primate that lives on floating islands of papyrus on a single Madagascan lake; they are quite common in UK zoos)
Conservation: Owston's civet (I know it is another Asian carnivore, but these animals depend upon conservation by zoos for their survival, so fit the concept perfectly)
I also figured, just for my own amusement more than anything, I would choose one new exhibit species for each pack (because I love the possible diversity of exhibit species):
Deluxe: King cobra (I don't think snakes will come with any DLC, so this is my way of adding what I see as the most important missing snake)
Arctic: Moor frog (a Eurasian frog that lives on the arctic tundra - the males turn bright blue during their breeding season)
South America: Collared treerunner (a quite colourful, arboreal lizard from the Amazon rainforest)
Australia: Frilled lizard (one of the main missing Australian exhibit animals, a highly charismatic species of reptile)
Aquatic: Atlantic mudskipper (would be the game's first fish, which would also work well with the current exhibits as it requires land and water)
Southeast Asia: Malaya giant weevil (a colourful insect that is among the largest weevils in the world and has been kept in zoos before)
Africa: Pancake tortoise (a small, critically endangered and quite commonly kept savannah tortoise)
North America: Common collared lizard (a brightly-coloured desert reptile that is fairly widespread across North America)
Europe: Olimpia's ground beetle (a beautiful and threatened beetle native to Italy that could use the same temperate exhibit as the fire salamander)
Wetlands: Common yabby (a vulnerable freshwater crayfish native to Australia that could be paired up with displays for platypus and saltwater crocodile)
Conservation: Turquoise dwarf gecko (a critically endangered African reptile that would add a new African species)