The Warlock Class Order Hall is definitely straight out of the Burning Legion design.
The Warlock Hall is located inside of a rift within the Twisting Nether called the Dreadscar Rift, which you take over during your Class Hall Acquisition questline.
Once you have completed the quest chain to get this class hall, you can find the portal to the Dreadscar Rift in the Underbelly of Dalaran. Several Notable NPCs can be found here walking throughout the rift.
Here’s a thorough walk-through of the Warlock Class Order Hall.