all taken from link below, it's very important stuff so I copy it here
http://eu.battle.net/forums/en/wow/topic/17613722206
To make it concise and keep to the facts:
- you can upgrade (one? two? many?) legendaries in 7.1
- this comes as a quest - non-repeatable...
- you need to collect 50 Essence of Whatever from Nighthold bosses, so yeah, it'll be quite the grind I assume
And now we reach our complication: if you have a good legendary - you are safe. You know you have to upgrade it, and you'll be done. If you don't have any legendaries, or have a bad one, you will be put in a very bad situation:
- no legendary, nothing to upgrade, /cry alone in a corner and be behind the "lucky" dudes and those that profited from bugs, simple eh?
- bad legendary - you either upgrade your !@#$ legendary (for example the stupid shield neck), and after your weeks/months long effort... good legendary might drop and you cannot upgrade it (most probable case, seeing as the quest is one time only), or you need to do again the 50 Essence of Crap thing - if we're "lucky" and the quest can be repeated.
- you don't upgrade the bad legendary and keep the quest reward item that allows ONE legendary to be upgraded, and still hope for RNG to give it to you. This, however, has its own set of disadvantages, as you basically pass on a 925 item with inflated stats.
Meanwhile, lucky dude with BiS legendaries will just upgrade their best and have nothing to fear, further extending the gap between lucky/non lucky.
For how long must we suffer the pure dumbness and atrocity of this RNG system that has NOTHING to do in WoW?