I have yet to see a website sporting this information that gives us anymore information on the origins, other then to say that it's "according to sources". The closest thing that I've found to a "source" is that masks resembling Worgen and Goblin were found in the WoW data when data-mined.
Blizz knows that the data gets rooted through a lot, and I really can't see them being stupid enough to let something like this slip so easily - It would be stupid to patch anything from the next expansion in at all at this point.
What I have found with through looking around is that Blizzard has trademarked the name "Cataclysm" which I think was a brilliant decision in timing on their part, with Blizzcon being so close, and fans being so curious.
Quote From WoWWiki:
The Great Sundering, also known as simply the Sundering or the Cataclysm,WRPG 185, 211 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.
All the same, it could be the unannounced new game, or something entirely different. I think that most of these websites are going too far out on a limb and making wild speculations.