In the QuakeCon video they showed armor for both Assassin guilds. The Dark Brotherhood most likely came about when they splintered off from the Morag Tong after they assassinated Emperor Reman III--250 years before ESO takes place. Naryu Varian is a main character in EP and is one of only a few remaining members of the Morag Tong.
Morag Tong
The Morag Tong is an ancient guild of assassins headquartered in Morrowind, celebrating murder in the name of Mephala. They have been active since at least the First Era, and their targets have included multiple rulers of Tamriel, high-ranking Dunmer nobility, and countless others. The Morag Tong is unique in its sanctioned status under the Morrowind government to perform legal executions, bound under contracts called 'writs', although extralegal 'gray writs' are rumored to exist.
Morag Tong Armor

Morag Tong Weapons
http://www.uesp.net/wiki/Lore:Morag_TongDark Brotherhood
The Dark Brotherhood is a guild of assassins shrouded in shadow and mystery which has been active all over Tamriel. While their business is certainly not legal, their existence has typically been tolerated or ignored.Whenever an individual with legal authority takes an interest in their dealings, the Brotherhood relies upon a combination of bribery, blackmail, coercion, and murder to keep their activities hidden. They have been bitter rivals of the Morag Tong since the Second Era. The Brotherhood is also known for their worship of the Dread Father Sithis.Dark Sisters are accepted into the Brotherhood as equally as Dark Brothers, though members of either gender are often referred to as Brothers.
Dark Brotherhood Armor

Dark Brotherhood Weapons
http://www.uesp.net/wiki/Lore:Dark_Brotherhood
Do you think they will add one or both as join-able factions?
Which would you rather join???
Edited by Enkil on July 19, 2014 1:44PM