A WoW DB Entry shows a new item found in the version 5.4 patch on the Public Test Realm for World of Warcraft called the "Enduring Elixir of Wisdom" which is sold from within the MMORPG to provide double XP, saying simply: "Experience gained from killing monsters and completing quests increased by 100%." This continues a steady trend over the life of the game to make leveling up quicker, though this would be the first chance to pay to not play the game. A blue post from Blizzard also explains they are testing the ability to make in-game purchases: "We are currently exploring the possibility of adding a way for players in certain regions to make purchases directly within the game. As part of this process, elements related to this will be appearing on the PTR. We’ll provide additional updates on our plans as development progresses." Thanks Blend Games.