Some interesting news at last.
This info comes from Momocon 2013, where Sifu Kisu (Martial Arts Consultants, Sifu Manny (Toph bending consultant) and Steve Blum (Voice of Amon) were in attendance and had a panel.
Naturally Korra questions were asked and answers were given. Thanks to Fangirlyfashionista on Tumblr we know what was said.
The first thing to note is that nothing was outright confirmed to appear, just hints. So while likely, they are not facts.
-We will see the sub bending of Airbending. The one element as of now that has no alternate ability will at last get covered.
Firstly, we’re gonna be getting a sub-bending form of airbending! Kisu said it was going to blow our minds.-Sifu Kisu knows who Lin's father is, meaning that it will be more than likely be revealed in upcoming episodes.
Also, he totally knows who Lin’s daddy is, but he was tight-lipped, so we’re gonna find out soon enough I’m sure.We also do not know if these will be Book 2 things or not, just that they will more than likely be explored in future episodes. Thoughts ?