James Cameron says he already has plans for 6 and 7

Looks like he's aiming to equal the Star Wars saga

and why not. people love CGI.

I have ideas for 8, 9, and 10:

8: save the rain forrests on Pandora, bro
9: save the ozone on Pandora, bro
10: save the spotted leopard seal on Pandora, bro
11: stamp out nuclear reactors on Pandora, bro
12: give a hoot, don't pollute on Pandora, bro
13: only you can prevent forrest fires on Pandora, Bro
14: PLM Pandoraian Lives Matter, bro
15: Pandora government is run by reptillians, bro
16: the "landing on Pandora" hoax, bro

these should pull in BILLIONS!!!

Why not. With all the technology infrastructure established, which I believe number 2 here already paid for, these things must be virtually free to produce. They're just printing money now.