I highly doubt that we'd ever see a SF version of Avatar but it's always nice to speculate. Given 10.000 of technological advance i doubt the Avatar would have much power anymore at least not in the fighting category. Much of their power can be easily countered by technology.. normal fire is meaningless for a full body combat suit (think something like Iron Man) as well as water based powers (Ice as the hardest thing water can produce?). About the only thing halfway effective would be Earth and Air to unbalance the opponent but none of the standard bending practices could harm an armored soldier effectively. However the Avatar could still be the spiritual guide of humanity working as the bond between Spirits and Mankind and ensuring peace which is their purpose after all.