If you're looking for a summary of 2.1.0 changes, check the two posts in the menu
>>> Patch mirrors <<< (I suggest downloading only from well-known sites.)
What we said one (two ?) months ago is confirmed, you'll have to slay Al'ar in the Tempest Keep and talk to a guy in Serpentshrine Cavern (after slaying Fathom-Lord Karathress). Thanks to Arthyn from Vanquish for posting the screenshots on our forum.
There is also a Video of the event available.
"After killing Karathress, our guild was able to pick up a quest from Seer Olum. He spawned in the spot where Karathress stands. He gives a quest called The Secret Compromised which tells you to go to the Warden's Cage to talk to Akama. After a cutscene with a conversation between Seer Olum and Akama, Akama talks to Illidan. Illidan then tells Akama to kill Al'ar. Akama then gives you the quest Ruse of the Ashtongue which requires you to kill Al'ar wearing the Ashtongue Cowl. The Ashtongue Cowl gives you the appearance of an Ashtongue while in Tempest Keep. Upon using the Ashtongue Cowl in Tempest Keep, a buff called Ashtongue Ruse is applied to you giving you the appearance of an Ashtongue. The buff lasts through death but is removed when zoning. Screenshots of the conversation and what wearing the Ashtongue Cowl looks like:"
On a side note, it seems there is a decent amount of new loots added to tier 5 instances, new epic patterns and even armor parts. The two first loots are from Hydross, the last one is from the Black Stalker.