It's unclear what the title actually refers to, but BlizzPlanet has noticed that Blizzard has now trademarked the term "Cataclysm" with the United States Patent and Trademark Office. By the looks of it, it'll be used for the title of a game platform, an entirely new game (or expansion), and some sort of related merchandise.
MMORPG #2, perhaps? Or maybe a new World of Warcraft expansion pack?