Thanks to a new interview from Mike and Bryan on the first episode of the Nick Animation Podcast we have confirmation that the upcoming Korra comics have in fact been delayed. This has been a big rumour for a while as no additional news has come out since NYCC last year and the expected release date of Fall 2016 fast approaching.
"Those won't be out for another while, they got a little delayed" - Mike and Bryan
This is the quote from near the end of the podcast, it is Mike and Bryan speaking about it at the same time, so half of the above quote is from Mike and the other half Bryan.

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This is definitely disappointing news, but we don't know the full extent of the delay. We know Dark Horse are waiting until San Diego Comic Con in July to talk about the Korra comics again, but the silence up to now has been very frustrating. Rumours the past few months have been that the artist for the Korra comics who was confirmed at NYCC last year, Brittney Williams is no longer working on the project. This has not been officially confirmed, this is just rumoured. At this stage it looks like early 2017 at the earliest for the comics if they are delayed past the initial fall 2016 date. I just hope that they do give us some decent information at SDCC this year. I want covers, concept art, an idea of the story/character arcs to expect and maybe even a preview page. They obviously announced Korra comics last year at a super early stage, they need to deliver now. As for rest of the Mike and Bryan interview. It all depends on how many previous interviews you have heard with them before. Myself having listened to most of their major interviews had heard these questions and answers before so most of it was a repeat. If you have not heard the creators talking that much in the past you will probably learn a lot from this 40 minute interview. Don't go into this interview expecting Mike and Bryan to talk characters and plot, this is very much focused on how the process of how the shows were made.