James Cameron never fails to go for the gusto with his movie projects, so although it came as a surprise earlier this year when the news broke that Cameron intends to make three Avatar sequels back-to-back-to-back - rather than two followups, as was reportedly the original plan - it didn't exactly rock the industry or shock movie lovers around the world. (At least, not anymore than when Peter Jackson decided to turn The Hobbit into a trilogy after principal photography had wrapped - to cite an appropriate example for comparison.)
The second installment in the planned Avatar quadrilogy is expected to reach theaters by 2016, which is a year later than the film was originally slated to arrive. Leading man-turned-Na'vi Sam Worthington has lent further credibility to the new theatrical date, by revealing the expected start date for production on Avatar 2, followed thereafter by Avatar 3 and Avatar 4 (official subtitles - or lack thereof - TBD).
Worthington was recently on the breakfast show for Australian radio station Nova 96.9 (hat tip to Yahoo!), where he revealed that Avatar 2 will begin shooting by October 2014, with the third and fourth installment filming immediately thereafter; in total, principal photography should amount to about a year in length. The Avatar 2 portion of production could be the most physically strenuous for Worthington and his fellow cast members (including, Zoe Saldana back as Neytiri), since that film is supposed to take place in no small amount in the oceans of Pandora - and thus, will require revolutionary motion capture photography to create the all-digital underwater environment (just ask Sandra Bullock and George Clooney how easy it was acting in the similar all-digital version of space during production on Gravity).
Furthermore, Worthington indicated that Cameron has by and large finished with the screenwriting process on Avatar 2, since the filmmaker is currently head-down in the middle of pre-production and preparatory work a solid year before shooting begins. That makes sense, given that Cameron has also recruited four different screenwriters - Josh Friedman (War of the Worlds (2005)), husband-wife writing partners Rick Jaffa and Amanda Silver (Rise of the Planet of the Apes) and Shane Salerno (Armageddon) - to work on scripts for the Avatar sequels. Friedman is assisting on the Avatar 2 script, while the other writers help put together screenplays for Parts 3 and 4, respectively.
However, Cameron's approach makes it difficult to gauge when additional casting announcements will be made for the next three Avatar movies, seeing how much time we have until production actually commences. So far, we've gotten semi-official confirmation that Avatar leads Worthington and Saldana are getting ready to return in the new installments, alongside Sigourney Weaver in some as-yet unspecified capacity. However, the sole new casting addition rumor so far, Arnold Schwarzenegger, has been denied by Fox (which doesn't mean it's not true, though).
Avatar grossed nearly $2.8 billion in theaters worldwide and won a couple Oscars in the process, but thus far it feels like most of the interest in the sequels has been more oriented towards the doors they will open from a technological perspective - like how the underwater mo-cap photography in Avatar 2 will increase the odds of an Aquaman movie becoming a reality in the future - rather than, the content of the stories that Cameron intends to tell hereon out.
The creative achievements of Gravity has put even more pressure on Cameron to deliver a more captivating and innovative narrative this next round, since it will be more difficult for the films to coast on their technical accomplishments alone. In all fairness, though, the filmmaker is well aware that he needs to step his game up and make the next trip to Pandora (not to mention, the long delay until takeoff) seem worth it - and, frankly, at this point, everyone ought to know better than to bet against Cameron.
Avatar 2 is expected to reach theaters in December 2016, followed by Avatar 3 in 2017 and Avatar 4 in 2018.