It seems the final boss of Manaforge: Omega and the expansion has some extra goodies for Priests! Players have received a quest that rewards a new mace transmog appearance, which is an unused Legion artifact appearance!
A Curious Fragment
After defeating Dimensius on any difficulty, Priest players will receive an item that starts a new quest! 
A Curious Crystalline Fragment starts A Piece of the Past. The questline has players resurrecting others and defeating rares and elites throughout the War Within zones. At the end they’re rewarded with 
T’uure, Remnant of the Naaru, which is a recolor of T’uure, Beacon of the Naaru, the Legion Holy Priest artifact. Here’s what it looks like:
Perhaps there’s more unique transmogs for other classes hidden throughout K’aresh?