Enduring Elixir of Wisdom is an elixir that increases experience gained from killing monsters and completing quests by 100%. Wow, that's quite the buff, right? But not really stop the presses news? Wait until you hear the rest. It's currently listed as coming from the "5.4 In-Game Store". Yes, that's right, at the moment all signs point to this being purchased via a microtransaction.
Now, we didn't even know about the in-game store. Maybe they mean the battle.net shop, maybe they don't, but this is a controversial step by Blizzard if the datamining turns out to be accurate. Of course, leveling isn't exactly an onerous task, but nonetheless, exchanging what might be real money for faster leveling would add considerable convenience.
Do remember that this is datamining. It might not be accurate, it might be a placeholder, it might come to nothing at all.