Following a short two weeks since the unlocking of the last section of the Icecrown Citadel raid, the Plagueworks, we have learned that the next section, the Crimson Hall is now available for plundering.

Some brief details on the Crimson Hall from the official Icecrown Citadel page:

The Crimson Hall contains the leaders of the San'layn, undead blood elves who oversee the Scourge's operations throughout Azeroth. The blood-princes Valanar, Keleseth, and Taldaram were raised into undeath by the Lich King to avenge themselves while protecting their blood-queen, Lana'thel.