I also don't really see Cameron doing a Gaia-related story. Without the whole bio-net shebang, invoking a planetary spirit would entirely depart from sci-fi into space fantasy. I know Jake says something to the effect of "we humans killed our world spirit", but I'm not sure that was meant to be taken literally.
I will bet you a shiny new flying car that he does, because we'll totally have those by the distant future of 2018 according to scifi.
