Which to me means two things:
A: They have no plan to design a system for new animations etc for birds - habitat birds would be alright, but they seem reluctant to add them in unless they're a penguin or ratite. (aside from the RCC of course)
B: they've been working on a lot of this behind the scenes and intend to really wow us with it. It wouldn't have to be all in one pack, but to me it would make sense for it to be at this point.
Of course, if they were doing option B, if they wanted to...give us some confirmation without being completely official about more birds coming in the future, they'd put one in the walk through exhibits. Unless of course, that's exactly what they were doing with bats and butterflies, to test the flying system and show us that it's actually possible.