Blizzard has responded to patch testers' reports that a "100% XP buff" would be available from the "Game Store". The post indicates that Blizzard is considering a microtransaction store but that no firm decision has been made.
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.