Here is the article from IGN where they interview Mike and Bryan and some of the cast about what is to come in Book 2. I will point out the main things using the magic things that are BULLET POINTS
  • Mako has joined the Republic City Police Force as a cop, which suggests that the police has opened to not just metalbenders, he is making a name for himself busting the triads.
  • Hiroshi is in prison
  • Mike and Bryan wanted to get away from Korra training as that was explored in ATLA, and focus more on Korra adapting to her role as a fully realised Avatar. They describe her as a "bull in a china shop" at present, she is going to have to learn how to really respect her abilities and role I think is what they are getting at.
  • We may see more appearances from Avatar Aang
  • Mike says  "We have the most flashback-y of flashbacks coming up" Bryan then hints that it will be deep into the mythology of Avatar and the legacy of the Avatar
  • Book 2 will have more romance
  • Mako and Korra are together, but with both of them in important positions their relationship can get a bit complicated
  • Bolin is going to have a bizzare love story
Check out the full interview in the link above for the rest. But all of this is the main new stuff. I for one am definitely more pumped for Book 2 now, all these little teases. What are you thoughts on this interview ?