Coming from a DAK CM...
1) Avatar focuses more on the effects of humans on the land. Yeah, I know conservation is the main message of the park, but the focus really should be on the diversity of Animals, and not new movie franchises. Sure I'm excited to see how the expansion will turn out, but it's like slapping Harry Potter in USF to me (awful comparison, but bear with me).
2) Ok, so I know there's a dragon in the original logo, there's a dragon on the ticket booth in the front of the park, etc., but does Animal Kingdom really need another section that focuses on something that doesn't currently exist? Yeah sure, it'd be cool to have something about mythical creatures and the possibilities for dragon attractions are endless, but resources are better used towards something that'd improve the park while moving towards the goal of having multiple themed lands filled with animals from around the (current) world.
3) This brings me to Australia. I see no reason as to why this hasn't happened yet. I trust Imagineering with finding awesome ideas for attractions in an Australian-themed land. Plus, it would almost complete the park, in having animals from every continent represented with top-class attractions. After that, it's just waiting for a South American-themed land.