1. Other Airbenders
No matter how many times you watch the trailer, there is no escaping one fact: there are now air-benders other than Aangs extended family. You can look for air-bending machines like those Teo invented in ATLA, but those are simply not present. So, unless we assume that Aang had some ladies on the side, which is extremely unlikely, we must accept that there are more air-benders. This could be chalked up to the fact that Korra opened both spirit portals, which could have possibly given more people bending abilities, therefore restoring balance to the world. Anyway you spin it; air-bending will be big in Book Three of LOK. There is a large number of air-benders wearing green Earth Kingdom clothes, including one who appears to be practicing bending with Korra. In one shot, Tenzin leads a group of people dressed in air-bender garb in meditation in front of what looks like an air temple. We also see Bumi, the unfortunate non-bender in Aangs family, finally getting his due, as it appears that he also acquires the ability to airbend.