I think one of the reasons there has never been an official avatar RPG system is that while Avatar has a great setting it isn't one full of factions or races in conflict.

Apart from humans (which suffer from balance issues) there aren't any other factions you could fight in an Avatar RPG, apart from wildlife. Without a lot of stuff going on its hard to produce a setting that stories can be told.

How would you add conflict to the world of avatar to provide lots of content?