Special effects work might delay movie . . .
Here’s what producer Jon Landau had to say:
“We’re not naming dates, but I think 2014 will be a tough date for us to make. It’s about getting it right. Movies make release dates; release dates don’t make movies. We’ve started already. WETA are already working and we have our core team working with us. And we’re working on underwater performance-capture. It’s going to be like the Floating Mountains in the first movie. It’s not going to be all underwater; it’s going to be a place we go to, leave and come back to.”
Avatar was released in 2009.
(Incidentally IMDb.com supplies 2016 as the sequel’s release date.)