Patch 5.4 - Legendary Quest Line Update
Wrathion is back again in Patch 5.4, first asking you to meet him at the Tavern. He has learned of the new Timeless Isle added in Patch 5.4 and wants to further augment your cloak by "time-locking" it.
You will have to head to Timeless Isle and collect 50 x Timeless Coin for one step in the quest. While you are doing that, you also have to defeat the four August Celestials of Pandaria in combat, which likely requires a group.
Once you have completed both steps, you head to the Seat of Knowledge so that Wrathion can augment your cloak once more. This will likely use the upgraded cloak models added a few patches ago.
After having your cloak upgraded, there is one final quest to kill Garrosh. Wrathion reveals to you that this was his plan all along, but he has no more rewards for you. The Golden Lotus may have a reward for you though, but the current rewards on the quest are just placeholders.
So far it's nothing special, and there's no reward. Hopefully, this changes as this quest line has been irritating at some parts.