Most details are in the article ^
Reddit source of images: https://www.reddit.com/r/TheLastAirbender/comments/1hi2tte/more_confirmation_on_the_leaks_this_was_using_the/
I find this interesting! Post apocalyptic is a good way to “reset” the world, and the idea of twin Avatars has been batted around the fandom for some time.
my advice is stay off reddit. the entire site tends to be a bit of a cesspool when it comes to any fandom.
just keep it to places that actually matter like here.