New Leveling Method, 50-60, 150% Damage and Huge Healing Buff (Patreon)

EDIT: Fixed The quest "Land Of Opportunity"  is at the end of the introductory series of quests in Maldraxxus in the Theater of Pain. This quest is on the main Shadowlands questline: it is not available using the Threads Of Fate alternative. This quest requires you to fight a champion, which when defeated sees you taken away from the area by Draka on a flying mount.

If you exit this vehicle you will remain in the Theater of Pain with a number of endlessly re-spawning mobs that award full xp. You also gain the buff "Rising Champion". This stacks up to 30 (one per npc kill) and gives you an enormous amount of extra damage and healing-I found it impossible to die even if I went afk with numerous mobs on me.  

This appears to be the fastest basic method yet for leveling from 50-56, at least for  classes/specs with aoe, and is easy to set up and maintain. The only major negative is that it requires you to level through Bastion first. 

EDIT: Experience gains seems to slow after level 56 due to the static nature of the mobs level. For some specs/classes alternative methods may become optimal at this point.