Likely next movies are an adaptation on the manga Battle Angel, which will use the technological tricks of Avatar. Forbidden Planet is also possible.
the tricky scenes are where you're blending live-action photography, stereoscopic photography and CG
The Internet Movie database has a 2011 release for Battle Angel with Cameron as the director
Battle Angel on wikipedia
The series is set in the future and focuses on Alita, a cyborg who has lost all memories and is found in a garbage heap by a cybernetics doctor who rebuilds and takes care of her. She discovers that there is one thing she remembers, the legendary cyborg martial art Panzer Kunst, which leads to her becoming a Hunter Warrior or bounty hunter. The story traces Alita's attempts to rediscover her past and the characters whose lifes she impacts on her journey. The manga series is continued in Battle Angel Alita: Last Order.
The Internet Movie database lists the following movies in development with possible James Cameron involvement
Cameron, meanwhile, confirmed that he is producing and developing a script for—but will not direct—a new version of the classic sci-fi movie Fantastic Voyage, which he promised will be "very different."
Earlier this month, word began to circulate that Cameron went gaga over a Forbidden Planet script from "Babylon 5" creator J. Michael Straczynski, who described it as neither a remake, nor a reimagining, nor exactly a prequel. Was this true? Would Cameron direct or just produce? Cameron: "That's a project that I'm actively involved in, but I haven't made any decisions about it yet.
Here is a youtube of Battle Angel rendered in 3D CG.
A non-mega movie would be Dive. "Dive" is the true story of a Cuban free diver who trains and falls in love with a French woman who breaks a bunch of world records before dying during a competition.
Battle Angel fan page