Despite the date, the Starcraft 2: Legacy of the Void beta has really launched. The third part of the RTS sequel is now available for testing to a select few players, based on Blizzard's magical metrics—or "system specs, recent StarCraft II activity, and an element of luck," as they put it. The beta includes a bunch of new units and changes, all of which you can read about here.
"At the start of the beta test, we will be directly flagging Battle.net accounts for access and will not be sending beta keys until later on in the beta cycle," writes Blizzard. You can check to see if your account has been flagged for beta by checking your Battle.net Game Accounts list. If flagged, you can download the beta by selecting "Beta: Legacy of the Void" from the Region / Account dropdown menu found in Starcraft 2's Battle.net Launcher tab.
New units so far include the Terran Cyclone, a ranged unit that attacks both air and ground units; the Zerg Lurker, a tier-II siege unit; and the 'Toss Adept, a "slow-moving harassment unit". If you want to see all that in action but don't have the Legacy of the Void beta, you can at least watch those who do streaming it through Twitch.