In certain unnamed regions
A "100% XP Buff" item that references the "5.4 In Game Store" was discovered on the World of Warcraft Public Test Realm, prompting players to ask Blizzard what the deal is on the forums.
"We are currently exploring the possibility of adding a way for players in certain regions to make purchases directly within the game," wrote community manager Zarhym. "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."
Naturally, Blizzard has come under fire for potentially introducing in-game microtransactions while still charging players for a monthly subscription. Something's got to give! I guess we'll see if this pans out and for which regions -- it's possible we'll remain unaffected in the US and Europe.