I hope the story covers some airbenders that don't join up with the Air Nomad culture and instead settle in Republic City. One of the themes of the current series has been how the march of the Avatar world into the modern era has come along with a breaking down of the old social order represented by the four separate nations.
I also half-expect that before the end of the season we will see one of the main characters learn how to bend a second element as an even more drastic consequence of Change brought on by the harmonic convergence and the greater impact of spirits in the world. Afterall the Avatar is the only one who can master all four elements, but why not having a limited subset of people who can now master two?
Then again I also like the notion that in counterpoint to the material of season one there are no "non-benders" in the world but rather everyone can bend but might not be aware of what they can bend. Perhaps some people are metal benders who aren't earth benders for example.