As we all know, Bryan and Mike are now helming a new, live-action adaptation of Avatar: The Last Airbender. While news has been slow on it, Bryan especially does post updates, and I figured I'd consolidate them all here. This blog will be updated periodically so I'd check back every couple of months or so.
08/28/18: Possibly, a VFX test for the new series may have happened. If /u/bonanzarama is to be trusted, tests of the Fire Nation Throne Room and Sokka and Katara in the Tundra have happened. While there is no doubt a project such as this happened, it is not officially confirmed whether or not this is related to Avatar. The "actor" for Ozai posted images stating he was working on an unnamed project and OP posted a call sheet from the day. More information can be found at the reference, be careful what you trust.
05/29/19: Bryan updated that they are still strongly in the pre-production phase. They're writing and planning and assert that Netflix is being very patient with them and they want to get everything right. They do not want to mess up, and they have high ambitions ("a fantasy travel show with tons of VFX, CG creatures, martial arts, etc."). They also said when they announced ATLA and TLOK they were much further along in production. They still have not started casting. Oh, and Appa will be cute. 
01/03/19: Bryan posted to his social media stating that they have not started casting, but when they do, they will have an open casting call for people to audition, probably this year. Don't waste your time DM'ing them till then.
- ↑ https://deadline.com/2018/09/avatar-the-last-airbender-live-action-series-netflix-1202467089/
- ↑ https://www.reddit.com/r/TheLastAirbender/comments/cwbysa/i_got_a_chance_to_work_on_a_visual_effects_test/
- ↑ https://bryankonietzko.tumblr.com/post/185226114707/mike-and-brandon-walking-between-meetings-from-a
- ↑ https://bryankonietzko.tumblr.com/post/181691530422/to-everyone-interested-in-auditioning-for-the