Some of my ideas:
Himalaya exhibit of two artificial mountains/hills. Visitors go along the valley in between, with suspended bridge and to the waterfall. Species are mountain sheep and goats, snow leopards, yaks and Asian brown bears. Visitors can also go on top of the rocks and see the panorama of the zoo.
Indoor hall with hippos, crocodiles and African waterbirds, imitating Okavango delta.
Indoor hall with underwater viewing of botos, giant otter and manatees, and other animals of the Amazon.
And somewhere on zoochat is my old exhibit concept for Arctic animals, including viewing of polar bears from the artificial ship surrounded by water. One commenter priced it at over $100m.
And maybe not impossible: several aviaries with ungulates.
One is Pantanal, with hiacinth macaws, assorted wading birds, capybara, tapir and giant anteater.
Another is Ethiopian Simien mountains, with gelada, ibex, vultures, marabous and ground hornbills. It is partially walktrough aviary, where visitors have vultures flying overhead and look on gelada and ibex across the stream. Then there is a close-up view through the glass. Then visitors enter a cave/narrow canyon, and see gelada indoor quarters. Then they walk outside the cave, and see the open-air pat of the exhibit. Geladas and ibex can enter there through the narrow tunnell. On the visitor side, there is a grassy hillside, where there are also free-living rock hyraxes.