Blackwing Lair will be released in the next content patch within the next two-to-three weeks, to be expected by the end of June or beginning of July, as reported by Jeff Kaplan(Tigole)—World of Warcraft Quest Designer:
“We had the final Blackwing Lair playtest on Monday at which time the dungeon was “locked out” and sent through the QA process so it can be delivered to you guys. So I wanted to give an early head’s up that Blackwing is on the horizon and should be in-game in the near future. Keep in mind, there are other things that can hold up a patch. I would expect Blackwing to be delivered to you guys around the end of June or early July. That’s my rough estimate at least.
As for Zul’Gurub, the zone is making great progress. We’ve recently re-lit the zone and replaced many of the buildings in there. I’ve seen people release screenshots of the zone that they’ve obtained by cheating their way in (this will get you banned btw!) but I think everyone will be pleasantly surprised to see the actual zone when it is live. The item and quest guys have some real challenges with this zone. Their goal is to keep all of the items and quests for the top end dungeons relevant while still making Zul’Gurub items desirable. Yet at the same time, the Zul’Gurub quests and items cannot outshine the Molten Core and above loot.
Some of the boss fights are really cool, as well. We had a ton of fun designing them and we’re really looking forward to getting them out there for you guys.
The dungeon and raid team has also been working on some “top secret” stuff that you’ll probably hear about soon.
But in the meantime, Blackwing Lair and Zul’Gurub are not that far off!”
Recently, Blizzard offered a Full preview of Blackwing Lair.