Implement a disease or a genetic conditions where animals become hairless/featherless.
Have animals be trainable for shows!
Have a vehicle the player themselves can drive with, or play with the zoo animals like kicking a ball (would be species specific and would not work with, say, crocodiles).
Revamp the way interspecies animals interact with one another (ie, when I put a hyena within an antilope's viscinity).
Would be lovely to get more guest interactables like playgrounds - swingsets, merrygorides, slides.
This would be much more important than adding more animals, for me.
Not viable for the current state of the game, but I would love (I am very bird centric):
Helmeted hornbill
Saint Vincent amazon (or a different species most commonly known as Blue Fronted/YH amazon)
Eurasian griffon
Kea
Bearded vulture
Magnificient riflebird (or any Bird-of-Paradise, if I may be vague)
Mexican hairless dog (a primitive dog breed, but unfortunately for this list is a domestic dog)
"Ambient" animals:
eurasian/red/fox squirrel
brown rat
rock dove/domestic pigeon
raven
starling
eurasian reed warbler
Future DLC (very generic list):
1. Marabou stork (at the current state would be the animal I would want the most to be implemented in this game, very beautiful creature)
2. Aye-Aye
3. Mallard/Mandarin Duck
4. Honey Badger
5. Chameleons if the exhibit system is revamped.
6. Gerenuk
--For ZT2 tradition's sake, not necessarily for me:
Blackbuck
Musk Ox
Having iguanas and snakes be able to walk, or slither, outside exhibits.
Misc. plants:
Fluorescent plants!
Carnivorous plants like sarracenia, more types of nepenthes.
Many colours of heuchera plants.
Orchid species like catasetum, paphiopedilum
Black bat flower
There are so many funky looking succulents and cacti out there like the Anacampseros papyracea, (my example plant is probably too small to be practical enough here, but you get the gist)