The engine of Planet Zoo is backward that causing stuck when you have more than 20 habitats, the pathing system is also notoriously ****** that often demotivates new players. There is no innovative attraction after Twilight pack, the Frontier definitively knows the players' desire for flying birds and aquarium, but the innate defects of the system may not run the aviary and aquarium well. If we want to bring out more potentials from this game, a new developed system is required, which probably needs a new game, PZ2. I would say I am OK that the Frontier ends the support this year, as long as they put the effort on the PZ2 with the advanced system.
I don't think the Frontier will offer innovative things like Aviary at the end of support, probably just animal pack. I guess it might be a Safari pack that contains species from Africa, South America and South Asia. The Frontier is facing financial hardship now and has laid off some staff since last year, they probably don't have enough resources to work on new models, most species offered by the last packs are more likely easy clones (like antelopes, Nile Crocodiles, Sulcata Tortoise and some felines)