I hope the dvd is released with a lot of behind the scenes info. Like, what specific cultures the nations are based off in the movie, inspirations for certain stuff (weapons, clothing, landscape/terrain, etc.) I also think it would be cool if they showed what martial arts were used, inspiration for bending effects (how do you show what air moving looks like). I know several of the topics have already been discussed or addressed with the M. Night interviews and stuff, but, I think it would be really cool if they went much more in depth about it.
Something like the LOTR extended edition movies would be cool too.