If there's any pack that should be "super sized" it's an avian pack. For #1 because it brings in a new area of the animal kingdom that has yet to be explored (not counting non-flying birds or the Flamingo/Peafowl which do fly IRL, but are mostly ground oriented). For #2 while birds do all come in all sizes and don't all look the same, the diversity of the skeletal and muscular structure, the basic things I would imagine the animal rigs are built around, are not as diverse as what's in the game now. Sure, you have your long thing wading birds, which are going to be a different build than your large birds of prey, which will be different than your smaller more traditional build of birds, but there's not so much diversity that Frontier could not use the same basic rig for quite a few animals. - Cranes, herons, Storks, Ibises, they could all use the same base rig which would then have individual modifications, just as one example. Then you have your Secretary Bird....which is kind of an anomaly I guess, that due to their spastic running would probably be fairly rare to have repeated in other species.
I just can't imagine they'd do an avian pack and give us less than 8 animals, possibly no exhibit animals. The 4 +1 model would be really disappointing now that they've shown they can do a larger animal pack. 8 birds...at minimum. And if they wanted to double that and charge extra, well, I know I don't speak for everyone in this regard, but I'd have no problems paying a good bit more for 15-20 birds.