The BETA has launched and Blizzard is currently testing it's servers to make sure their new platform is running smoothly. Blizzard always takes a little longer to launch their titles and given that they really want to nail their new BattleNet platform, I'd say the BETA will be tested for a good 4-6 months as they fix/patch bugs with the live community. After that, I'd give them another 6-12 months to do final touch-ups.
My guess is Q1 2013.