At the Korra panel at Momocon, the guests (Amon's VA Steve Blum, Sifu Kisu (martial arts master), and Sifu Rodriguez (consultant for Toph)) were present for a Q&A session. There they revealled that Kisu actually knew who Lin Beifong's father was and that season two will involve a new subsection of airbending being explored. Whether the new bending style will be akin to metalbending or something more sinister like bloodbending, remains to be seen.
Two days later, the new airbending and news that Lin's dad will be revealled were confirmed, though not necessarily for season two.
Finally, Book Two has no official release date yet, despite post-production having just starting to wrap up fairly recently. This is more down to Nickelodeon than the creators of the show though. Ah well, when it comes it comes.