Moroes was added as a Class Hall Champion in patch 7.1 along with him as a boss in Karazhan. Any class and faction can get him as a Class Hall Champion, but unlocking him require some bits of luck.
The first step involves killing him in Karazhan and hope that an item called "Broken Pocket Watch" drops. This items begin a quest called Master of the House, which is the quest you need to complete to unlock him. This need you to collect the following four items:
1) Exquisitely Stinky Cheese. Obtained from a mission at the Class Hall.
2) Falanaar Fine Vintage. Obtained from a mission at the Class Hall.
3) Spiced Rib Roast. Created by cooking it, or just buy it from the Auction House.
4) Master's Bell. This is dropped by Shade of Medivh in Karazhan.
Once you have all four items, go to the cemetery outside of Karazhan and turn in the quest. This opens up a new quest you can turn in at the same time, which awards Moroes as a Class Hall Champion.