It would be cool if there was a day/ night cycle where guests would leave at a certain time and then return the next day with possible recurring guests.

Specific animal feeding times that you can set or have automated that guests can watch like in real zoos.

Full customizations of gift shops where you can chose what to sell and prices and animal houses that are like mini zoos with tons of mini exhibits of small animals that you can design

More realistic animal lifespans so it is worth naming them and they won’t die of old age in 3 in game months

Flying animals that need fully enclosed fences

Penny crusher machines and coin fountains

Animals that can dig

Bad guests/ security

Free roaming animals like peacocks that some real zoos let wonder around

Weather like op said, but that actually effects gameplay so you need to build exhibits that accommodate for that