A data mine for World of Warcraft patch 8.3 on PTR has revealed some details regarding items and the Death Knight.
The first item relates to N’lyeth, Sliver of N’Zoth, indicating a new toy and title. It appears that attacking your own faction members in World PvP with the help of N’lyeth will net you with a toy and new title. Additionally, if you purchase the Black Dragonscale Backpack using Corrupted Memento, 40,000 to be exact, you’ll receive a cloak which resembles a backpack, but which can be transmogged.
New for Death Knights include an aesthetic tweak to the eyes making them glow. Additionally, the Veteran of the Fourth War ability for allied races and Pandaren Death Knights has been added.
Another detail includes the Mythic N’zoth raid. It seems like a secret last phase, called Forge of Fate, has been added. This supposedly follows the hidden Dungeon Journal entries from prior end bosses.
You can learn more about the data mine here.