A video just put up on Nick.com confirms October 3rd as the premiere date for the fourth and final "book" of The Legend of Korra. They're sticking with the digital distribution model, and a new episode will be posted to Nick.com every friday.
Well, on the one hand this kind of sucks, considering that this is going to be it for the Avatar-verse, at least as far as we know for now (fingers crossed for a third and fourth series, right?), but on the other hand it is extremely exciting, since the ending of the last season, which shall remain unspoiled here, was, shall we say, extremely unexpected. Good to know we won't have to wait a whole year plus, even if this does indicate that Nick is pretty much just dropping what they've got left of the franchise, which doesn't bode well for its continuing health. Ah well. Book Four, October 3rd, get hyped!