It's really difficult to make any assumptions about how Frontier will add birds if indeed they ever decide to. Personally I'm in favour of having a number of different aviaries of different preset designs that function similarly to exhibits (except with the birds on looped animations rather than being mostly static), but that doesn't mean it will be that way. My opinion is basically based on the idea that if the birds behave as regular habitat animals, we might find ourselves having to compromise on what animals we add to the game. I love the exhibits as they are, because I can build a big reptile house without losing out on adding big habitat animals as well. If I had to design every little bit of the exhibit in the same way I design my habitats, it would likely slow the game down considerably, and I'd have to start picking and choosing between small exhibit animals and large habitat animals. A real zoo has both.
So it is with birds. I understand and appreciate that people want birds to act like habitat animals in some huge complex aviary-building system, but given the fact that there are already optimisation issues with the game as it is (if your zoo gets too big, or too busy, it suddenly starts to lag and the quality drops significantly), I can only imagine that adding in such a system for birds would make these problems a lot worse.
In any case we'll have to wait and see what Frontier does in the future. Many people are fairly confident that birds will come eventually. I think that if any zoo game was going to properly implement them, it would be Planet Zoo, but exactly how they will go about it is really up in the air. The only Frontier-specific example we have is the aviary in Jurassic World Evolution, which could turn out to be a good indicator of where they are heading with Planet Zoo.
