Why does everyone expect concept art now? The land isn't expected to break ground until next year. They still have a lot of design work to do. They probably don't want to show you art until everything(every little thing) is locked down. They don't want another Fantasyland situation where first art was released and then things changed.
The design process is very boring to be honest. It's just drawing after drawing. Test after test. I've been through this process(with other parks) before. It all starts out exciting, but it gets so boring to see similar drawings over and over again.
To put this all into perspective for you guys, many of the major rides in the industry take about two years to design. Some have taken as many as 5 years. So it's not surprising to me that we haven't seen any concept art.
BTW, he is a video of Cameron on creating the Avatar game. It's a different situation, but it does reflect how he collaborates.
http://www.youtube.com/watch?v=7IsfjoxheUU&list=FL-y0dAnyobIYlBH9vjQGNAw&index=25&feature=plpp_video