Reptilia:
1. Giant Girdled Lizard - would work in PZ - a grasslands lizard that lives in groups, another squamata that is not an exhibit animal or a monitor
2. Indian Narrow-headed Softshell Turtle - giant, mostly-aquatic freshwater turtle found in some zoos
Aves:
3. Red-crowned Crane - iconic crane species
4. Secretary Bird* - I find your lack of ground dwelling birds disturbing
Carnivora:
5. Spot-Necked Otter* - personal favorite, being more specific this time
6. Southern Sea Otter - also personal, but I'd say it has a greater case since we have a freshwater one
7. Leopard Seal - would be nice to get another Antarctic animal that is not a penguin.
8. Pallas Cat* - shifting focus onto small cats, and these are super unique and provide more central Asian animals, my next in line would be caracal
Artiodactyla:
9. Saiga - Asian plains bovid
10. Barasingha - Good for mixed species with peafowl, rhino, and elephant. Red Deer or Pere David's are good alternates.
11. Markhor - need to have more mountain species
12. Chacoan peccary - to round out pig species, preferred over other peccary due to conservation status, unique ecoregion, and physical features.
Perissodactyla:
13. Przewalksi's Wild Horse - most popular non-zebra equid.
Rodentia:
14. Capybara - largest rodent + another South American animals
Monotreme/Marsupials:
15. Platypus - this one speaks for itself
16. Short-beaked echidna - lets round out egg-laying mammals
17. Common Wombat - non macropod marsupial, personally prefer over Tasmanian devil
18. Goodfellow's Tree Kangaroo* - an arboreal macropod, switched from Matschie's on last list
Primata:
19. White-handed Gibbon - need a gibbon species, picked over Crested due to larger range over SE-Asia
20. Black Howler Monkey - another new world monkey