James Cameron is a difficult one to predict, yes Titanic and Avatar made huge numbers, but I mean... It is 'only' two movies of his whole filmography, and Cameron did capture a zeitgeist at those times which I don't necessarily feel he can this time. I don't think Cameron should be bet against, but equally I don't think it should be expected that he'll have another huge success on the level of Titanic and Avatar. Even my best friend, who loved Avatar, isn't excited for a sequel (though I know that's not necessarily what all Avatar fans think).