Why? The Game is feature complete and the talent trees are sadly fixated as well. Priest is a shitshow, but that's every time so, since the dev either run away while developing it or is simply incompetent; but that's sadly always the case. So why?
Just for the sake of: delaying = better? Also there is no chance in hell for a release on the holiday season. jan 3 or 10 is very unlikely. First window would be at earliest on the 17th, but that's also short before february is, and since developers seems all to be keen to release every game that ever existed on february next year, blizz would be stupid to have this kind of window.