This would actually be very cool, they could be awarded by having a certain total Item level (because GearScore is gay) or maybe completing an epic quest at Level 85 like in Vanilla.
Examples; feel free to add your own.
Druid: Archdruid <Name>
Mage: Archmage <Name>
Warlock: High Summoner <Name>
Hunter: <Name> the Big-Game Hunter
Paladin: <Name> of the Light
Priest: High Priest/Priestess <Name>