If I'm reading this latest James Cameron interview below correctly, then it now seems that the 'Future Earth' scenes are being incorporated into the 'finished'-quality extended DVD/Blu-ray version, after all! :)

Unlike the current 'AVATAR: Special Edition' theatrical re-release which has approx. 9 minutes extra, the 'Collector's Edition' DVD will include a version which has approx. 16 minutes extra added...including over 4 minutes worth of the 'Future Earth' opening. This is bound to be the definitive version, and these 'grimy cityscapes' should make for a dramatic contrast to the lush jungles of Pandora - http://www.oregonlive.com/movies/index.ssf/2010/08/interview_with_james_cameron_o.html