How much more of Pandora is there to explore?

Though the first Avatar briefly mentioned a few other clans of Na’vi and sections of Pandora, you got the sense the Omaticaya, the tree people, were the main Na’vi on Pandora. Now we know that’s not true. There’s also a water tribe, the Metkayina, which was so far away, they didn’t get involved the last time. With three more films left to go, what other tribes and landscapes will we explore on Pandora? People who live in the air? That can fly? What about the underground? The surrounding planets? We have no idea, but can’t wait to find out.