According to the Nick.com Official Message Boards, there is finally some information on the release date of TLA:LOK. According to the Message Board, Korra is set to come out this Spring! While no concrete date is given, I'm sure that this is as concrete as we'll get from Nick until the Kids' Choice Awards.
BTW, it also calls it Avatar: Legend of Korra and not The Last Airbender, although this could just be allowed for use on the website, since the website is international.
»Avatar: Legend Of Korra
»With the Hundred Year War long over, benders live harmoniously with non-benders in a bustling steampunk paradise called Republic City. Meanwhile, a bull-headed but incredibly talented 17-year-old Avatar named Korra is growing into her powers in Southern Water country. But how long can the peace really last, and what will happen when Korra escapes to the city and these worlds collide? You'll find out when Korra comes to Nick this Spring, but until then, keep on top of all the Avatar: Legend Of Korra gossip, right here!