Ok this probably will not be talked about in the final few shows but it should be addresed
Aang cannot possibly be the last air nomad. Bender sure, but last of his people no.
We all know there are 4 temples North and South to train Males and East and Western for females
Not all people in each nation can bend
so were do the nomads live? Giving the fact that the Air nation is a buddist like culture we can conclude that they are very free spirts
so if a member of that nation could not bend and were never taken to one of the temples to learn/enhance there ability and learn disciplne I think it would be safe to assume that they would just kind of wander the (earth) hence the name nomads and the fact that we know of no existing air (towns).
Book 2 episode 2-Cave of 2 lovers
sokka-"who are you?' -"I'm Char and this is my wife Lily, We're nomads happy to go wherever the wind takes us"
If Aang was the last air nation member he could not possibly restore balance to the world and with nobody to teach the new avatar airbending he/she (from the water nation) and the two after that (earth) and (fire), could exist but never be a true "Realized" avatar, then the next cycle would of course be air so with nobody there to fill the void the cycle would break
Hopefully this will be addresed some how in the final few episodes but unfortunitly I don't think it will