According to Eurogamer and their interview with Blizzard lead producer J. Allen Brack, the “players were not sufficiently advanced through the raid content that shipped with third expansion Cataclysm in December to handle the challenge of Firelands”. So myself along many others falsely predicted this raid coming out in 4.1. The interview says they’ll probably release it with patch 4.2, but they’re also considering having smaller content patches instead of just big ones. Of course, we’re still getting the new Zul’Aman and Zul’Gurub as 5 man heroic dungeons that will drop 353 item level loot.