I don't see them outright adding a new biome to PZ; the existing ones cover everything necessary (e.g. "wetlands" as a mix of aquatic, temperate, tropical, and maybe grassland). I would like to see some foliage gaps filled, though.
Wetlands Pack (bayou/Southern US building theme):
Capybara
Asian small-clawed otter
Barasingha
Roseate spoonbill
Common snapping turtle (exhibit)
Coastal Pack (large expansion of the existing Aquatic theme):
Crab-eating macaque
Sea otter
Little blue penguin
Brown pelican
Coconut crab (exhibit)
Alpine Pack (mining theme):
Gelada
Pallas's cat
Sichuan takin
Demoiselle crane
Alpine newt (exhibit)
Scrubland Pack (???):
Caracal
White-nosed coatimundi
Markhor
Rock hyrax
Veiled chameleon (exhibit)
Grassland Pack (gardening/zoo props):
Rocky mountain elk
Blackbuck
Przewalski's horse
Great bustard
European adder (exhibit)
A lot of these hypothetical packs suffer from the "no star animal" disease. The solution would probably be to mash two similar-ish themes together (e.g. a "waterways" pack combining wetland and coastal animals, a "drylands pack" that includes both true deserts and scrubland)