So after MoP, the people who earned a realm best time in any of the Challenge Mode dungeons got a FoS rewarding the title "Spiritwalker".
Is there any word out yet if there's a reward for the WoD equivalent?
I checked out the PTR, and the tab I assume it'll be in - legacy -> dungeons (iirc) - is completely empty and I haven't stumbled upon any word about it yet myself.
Watcher said here that they will not be adding any permanent titles for realm bests in WoD. While I don't agree with his decision, and I think they're just wasting some very nice titles (same way they wasted specific titles in MoP), this is the blue stance, and it's been known since before WoD's released.