Remeber a similar idea being kicked around back in the day. Maybe he'd become some master assassin for Azula trying to take down her father from the shadows. Then we get a heel to face turn when they have to hunt down and stop the Painted Lady terrorist.
Red Lotus comes into the good graces of the Avatar promoting the idea of having the nation's in conflict with each other being the best method. White Lotus plan and stake out the water tribes waiting for the next Avatar and make plans to train them in secret.
Future Tenzin is some military commander overseeing the boarders between the nations.