The original projected release date for Avatar 2 was late 2016, but a few months back Cameron announced the project won’t be ready until 2017, instead – having said that more time was need to develop the film, which is now part of a narrative saga (not a stand-alone sequel).
James Horner was interviewed and mentioned that James Cameron actually now has enough script material for four or possibly even five more films.
“[James Cameron’s] got four [‘Avatar’] sequels script-wise, and he’s trying to make it into three. And I think that’s where the effort is going right now […] how do you keep it from expanding into a fifth movie?”
And Cameron himself told AP:
We’re writing three simultaneously. And we’ve done that so that everything tracks throughout the three films. We’re not just going to do one and then make up another one and another one after that.
source Hey U Guys