I'm not convinced there are only 4 packs left. I get that support won't last forever, but there is so much to explore with PZ I think it will remain profitable to support and expand for a long time to come.I'm fine with domestic animals conceptually but there would be riots if it were included and we're indeed only getting four more packs.
Something I've thought for a while but not fully articulated is also that, for both aviaries and aquariums, I have a sense of "commit fully to it or don't do it at all". The real appeal of aviaries in real-life zoos is to have walkthrough buildings with dozens of species. An aquarium pack, unless it were meant to be a Seaworld-style focus only on large marine mammals, would also feel fundamentally incomplete if you only had four or even eight different fish. If Frontier can't do small flying birds right, I'd rather they be saved for a hypothetical PZ2 (or for the next zoo simulator game to take a crack at).
The least-bad solution for both more proper bird representation and not having to risk a "hollow" aviary system is just to add a lot of birds that don't need aviaries. Starters would be the three that score highly on the meta-wishlist (secretary bird, emu, grey crowned crane)
And yes, agreed on your points for aviaries and aquariums.