This is the big production update we are waiting for and thanks to Mike on Tumblr we now know that Book 3 is finished.

book3done

Mike posted on tumblr with an update after they had just finished the final sound mix of Book 3, in his post he said
Can’t believe we’ve finished an entire season’s worth of shows.
So there you have it, Book 3 is in the bag, all that is left to air it. Mike also expressed what we have known for some time that they do not control release dates and cannot really say much news-wise.
I know you are all excited to watch — believe me, we’re excited to share it with you! I wish I could say I had some news about Korra’s release date, but I’m sorry to say I don’t.
For me this is Mike's subtle way of letting everyone know, "Don't get mad at me, Nick decided when the show comes out, I just make it and it is done now" This really highlights that if we have to wait until SDCC for a date/trailer that it will be an unnecessary 1 and half month wait, especially for any sort of news. Now that Book 3 is done, Nick should put out news very soon. Don't just wait until SDCC. Thoughts?