It's been floated as an idea alongside the market for XP boost items. Right now, only being considered in Asia. I personally don't mind XP boosts if they're only available for current level tiers after an xpac's been live for a patch or so, to keep it from pressuring people to buy them and win the server/world first race or feel like they have to boost their levelling in order to be able to play with others.
But here's the rub: if they add such things, will they have any incentive whatsoever to do what they recently did and reduce the XP needed to get to level cap in current content tiers? Will they take the XP boost items into consideration when determining how steep the curve is to reach the next cap? Same with the idea of them selling charms. If they do that, would there ever be a nerf to how many are needed for roll tokens, or alternative ways added to get them, or nerfs to how many you get from the in-game ways?
My issue with them selling things like that is not the retail in and of itself, it's them encouraging you to do it by strongarming you with in-game slants. I'm not saying that is what Blizzard will do or would do. But to deny the possibility is just being naive, IMO. And as I've said before, the time to voice concerns is now, before such things get implemented, to try and influence things so they don't go down that road.