Tumblr just pointed out a VERY, VERY interesting fact.
After Ravaa, the one who was holding all of the elements, is ripped out of Korra, she's not a water bender. She's an airbender. Thoughts? Rewatching the last episode, and she does in fact use Airbending at 6:36, when jumping into the tree of life with Tenzin before she goes all blue-giant.