So apparently, in 7.2.5, demon hunters can get [Arsenal: The Warglaives of Azzinoth], allowing you to transmog the appearance to your artifact weapons!
According to Wowhead, you must first acquire both warglaives, main and off-hand, on one character. Then, when TimeWalking Raids open in 7.2.5, if you have the Feat of Strength for Warglaives of Azzinoth, kill Illidan and you can get the [Arsenal: The Warglaives of Azzinoth].
So start running Black Temple of any character you have that can equip the glaives.
Remember: you need both on the same toon for the feat of strength!