There are quite a lot of things I'd love to see added to a potential sequel - one of the primary ones is an update to the exhibits, but what I want is basically the same as what has been mentioned above, such as modular exhibits and a sort of diorama system for furnishing them (the one different thing I will add for the exhibits - make the base-game exhibit animals more diverse and realistic - make it so that two-thirds of the Australian exhibit species aren't similar looking snakes, we need more than four African exhibit species, way more than one Asian exhibit species, the titan beetle and goliath frog should be replaced - that sort of thing).
Aquariums
The addition of aquariums would be great. I would have some fishes appear in the basic exhibit (especially smaller, more fragile or threatened species) and others that could be mixed in a larger exhibit the size of the walkthrough exhibit. This could either be viewed from a glass window along one of the longer walls, or have a glass viewing tunnel go down the middle of it. For habitat aquatic animals, I would start out with freshwater fishes and maybe manatees further down the line.
Aviaries
I wouldn't mind if birds came as a sort of exhibit (I'd make it a 'covered display' rather than the walkthrough exhibit, so that birds not suitable for a walkthrough can be included), especially if some birds had the opportunity to be removed from the exhibit for either handling or for flight displays, which can also be customised.
Animal personalities
I know this was something that came up early on but was never elaborated upon in the game. I would say four personalities would suffice, with each bringing their own advantages and/or disadvantages:
- Relaxed - the vanilla personality, that is basically comfortable with anything.
- Curious - has lower shyness, but can have lower fertility and is less suitable for reintroduction to the wild.
- Timid - has elevated shyness and needs a more complex habitat, but has the most suitable personality for reintroduction to the wild.
- Assertive - has higher aggression and is less suited to walkthrough or mixed-species displays, but has higher fertility.
Obviously, in sandbox box the animal personalities can be turned off, in which case they all default to relaxed.
Training
This goes hand-in-hand with both the flight displays for exhibit birds and the animal personalities. Training walls can be placed along habitat fences or adjacent to the 'covered displays', where keepers then perform training with the animal. For the exhibit birds, it increases their happiness when they go for a flight display while for habitat animals the training can boost their happiness, mellow their personalities towards the 'relaxed' state and allows veterinarians to treat animals while still on-habitat, reducing the need for them to be transported to the vet centre.
Reintroduction updates
As the moment, Planet Zoo has a sort of Zoo Tycoon 2 view to reintroduction - press a button and that's it. In reality, reintroductions are a complex thing that can often fail. I would rather there be more work required (for instance, you would be unable to reintroduce an animal that has been sick recently), with the possibility open that a reintroduced animal can go missing. Obviously, this can be turned off in sandbox mode.
Nutrition customisation
This could serve almost like a minigame within the wider game and serve as an educational part to the game. A much wider variety of animal foods can be purchased and have to be stored in a variety of different buildings (for example, a chiller unit for meat and fish, or a more general feed store for hay, browse, fruits and vegetables).
Then, in the animal information window, the diets can be customised by adding or removing food items and controlling their quantities with a sliding scale. Get it right and you boost the animal's health and fertility, get it wrong and an animal may not breed or suffer health issues.
For sake of ease, I would probably make it so that diets are customisable to species level rather than to the individual level. And if it seems like too much work a new staff member, the nutritionist, can do the work for you.
This is inspired in no small part by some of the really rather poor 'preferred diets' for some of the current in-game species - if you fed an elephant primarily fruits and vegetables, or a chimpanzee primarily processed meat, you would have a very sick animal in a very short space of time.
