Ok if you needed any more official confirmation as this. I tweeted Greg Street and he answered.

@Ghostcrawler Hey Greg, at the Cataclysm launch in London. You mentioned to me there was a Silithus update on the cards. Still happening?

@nykylaihellray Sadly, not in the immediate future. You can probably tell we started on it.

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"The true horrors of the universe lie within humanity itself" - Satoshi Kon

http://cargocollective.com/deadletter
My dark designs

At least a Dustwallow update is all but confirmed. Either that or they're going to remove Dustwallow Marsh quests from the Loremaster Meta in 5.1.

Awe, Greg just broke my heart. At least I still have the soundtrack.

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Rationalizing the irrational since 2005.