Recent reports have surfaced revealing that Blizzard Entertainment, the studio behind WarCraft, StarCraft, and Diablo, filed three new trademarks based on the term "Cataclysm" last Friday. The first trademark deals with the term in relation to computer games and mouse pads, the second deals with entertainment services/online games, and the third deals with a large assortment of uses ranging from coloring books to greeting cards.
In addition to the development of their new multiplayer service, Battle.Net 2.0, Blizzard is currently working on no less than five titles. The three revealed titles are World of Warcraft (updates and expansions), StarCraft II, and Diablo III. The studio is also working on a new MMO, which will start off a fresh new franchise, and a mysterious fifth project.
While arguments could be made to fit "Cataclysm" into any of these titles, the best theory I've come across was by ShoeHornOPlenty0069 at Voodoo Extreme:
This could be leading to an expansion in the Maelstrom. The Great Sundering, also known as simply the Sundering or the Cataclysm was a world event which reshaped Azeroth approximately 10,000 years ago at the end of the War of the Ancients. This event was triggered due to the Well of Eternity being destroyed.
Prior to the Sundering, there was only one continent on Azeroth, referred to as Kalimdor. In the catastrophic explosion, eighty percent of the land mass was destroyed leaving behind the major continents and scattered islands that are known today: Northrend, Kezan, the Eastern Kingdoms, and the remnant still referred to as Kalimdor. The site of the Well of Eternity became a swirling vortex of power known as the Maelstrom.
Only time will tell, of course; but Blizzard's next media convention, BlizzCon 2009, is scheduled for August 21-22. A Blizzard representative has refused to comment at the current time.