Book 3 will be the first 13 episodes of season 2 (season 1 comprised of Book 1 with 12 episodes and Book 2 with 14).
Studio Mir will animate ALL of Book 3 (and 4).
Book 3 begins a “few weeks” after the events of Book 2. source
Metalbending Police chief Lin Beifong and her family will play a large role; “We’ve got great stuff planned for Lin and her family. It’s not right away, so don’t be mad if it doesn’t happen right away. Book 2, for the Lin fans…she’s not very heavily featured in Book 2, BUT, very heavily featured in Book 3” - Bryke during a book signing. source
Thematically, Book 3 is about “Korra dealing with the change of the world in this point in time. At the end of Book 2 she says it’s a new era. And it really is and we’re going to show how Harmonic Convergence and her battle with Unalaq and Vaatu kind of shifted the world a bit.”source
Grey DeLisle, who voiced Azula in ATLA and the scorpion spirit in the Korra Book 2 finale, will be voicing a “bad girl” in Book 3. This character will NOT be a firebender (and not necessarily evil or a villain). She will also play a waterbender who is now speculated to be this character. source
Alyson Stoner will voice a character named Opal. source
The giant vines Vaatu created in Republic City are still there and spirits now roam them! source
A Dutch trailer for Book 2 mistakenly including a few Book 3 scenes has aired. See it here. The following is all the information gathered from it:
A dragon will appear in Book 3, possibly ridden by Zuko.
Korra fights some White Lotus guards and men wearing green.
Team Avatar has an airship that they use to travel to a desert-like location.
Select Book 3 stills (many more can be found here):
Book 3 production progress:
All voice acting has been completed.
The first four episodes’ “Take 1 animation” has been completed. source → [UPDATE] all but the last few episodes of Book 3 are done! source
Many stills are being posted by Bryan, indicating that Book 3 will be here within a matter of months.
Bryan Konietzko: “The premiere date hasn’t been pinned down, but we are on track to airing Book 3 with MUCH less of a wait than the unfortunate one there was before Book 2 aired.” source
The title of Book 3 has been reported to be Shogun or Connections. These are both almost definitely not true.
Korra and Asami could bond and become better friends. source → [CONFIRMED]“Book 3 buddies.” source
Bryan has confirmed the current reigning monarch of the Earth Kingdom is an Earth Queen. Given that Book 3 is supposed to focus on Lin, many people have interpreted this together as an indication that the Earth Kingdom will be featured and this Earth Queen will appear in Book 3.
Furthermore, production on Book 4 is underway as well.
Book 4 is the confirmed end of the show, with 13 episodes.
Book 4 has completed the animatic stage of production. source
Jason Isaacs (Lucius Malfoy - Harry Potter, Zhao - ATLA), Jason Marsden, and Anne Heche have been added to the cast in at least one scene with Jinora. source
There is at least one scene with Katara and Korra. source
Hopefully with the shorter wait for Book 3, we will be getting more and more information soon!
This post will be updated with new information when it becomes available.
“My mission will always be to use Raava’s light spirit to guide the world toward peace and balance. Harmonic convergence has caused a shift in the planet’s energy. I can feel it. Things will never be the same again. We are entering a new age.”