Yes at long last news looks to be coming. A commercial on Nick for a special week next week where every day they will have a look behind the scenes at Nick's animation studio, including looks at upcoming shows including Korra. In this advert for the event we do get to see around 2 seconds or so of footage. But it is an excellent sign that we may get a clip or trailer next week. Here is a screenshot of Korra and the link to the video,

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