While I think we're getting birds and more flying animals eventually, I think we're going to get them in waves. First with the bat then the butterflies. What I'd like to see next is have the Titan Beetle, Goliath Beetle, Sacred Scarab and Giant Malaysian Leaf insects get an upgrade to having animations and being in the walk-through exhibits. They can fly too(except the female Malaysian leaf insect) but in short bursts. That way people that don't have the Twilight, Grassland, and/or the next pack(s) could actually use the walk-through exhibits.
And the DLC exhibit animals would be 3-5 rhinoceros beetles with the exact same new animations that the previously mentioned insects would get!
After that, a few song birds in the summer DLC and continuing to work their way up to bigger birds as we finish Frontier's support of PZ, Parrots next. Then full flight habitat birds like Raptors and Hornbills. With a new ground dwelling bird being the free aniversary animal(if we even get another) like the African crowned crane.