Since everyone’s got something to say about the datamined/vaguely confirmed in-game store that’s ostensibly coming in 5.4, I felt like I should drop my science on that matter.
XP Buff Potions: Being able to shorten the time it takes to get from level 1 to max level is a beneficial thing to the game as a whole, from helping out people who are altoholics to people who’ve got limited playtime to hardcore players looking to get an alt into the endgame quickly to fill a gap in the raid roster. Moreover, it’s something that’s completely meaningless AT endgame; having an XP buff doesn’t contribute to player power in a direct way.
Lesser Charms: People have been flipping tables over this ever since the confirmation came down the pipe, and I don’t understand why. Yes, Lesser Charms translate into bonus rolls. Yes, bonus rolls give you a chance at getting gear upgrades in raiding content. That’s a pretty convoluted path to gaining player power, though, and ultimately, the main thing that buying Lesser Charms gives you is saving you the trouble of farming them up through dailies and/or farming mobs on Pandaria/the Barrens.
To put it succinctly: if Lesser Charms translated so readily into player power, why would so many people be complaining about getting the fail bags?
A lot of people have talking about “well, if they sell this stuff in an in-game store, what’s to stop them from selling gear? I don’t want a pay-to-win game!” Blizzard has got exactly zero reason to make the game pay-to-win when the ultimate objective of almost every gameplay mode in the game is gear advancement. It would be incredibly hurtful for them to sell gear with stats, which is why this worry is fear-mongering nonsense.
As for other stuff like transmoggable armor sets, mounts, pets — I feel like all of this is fair game. Paying for cosmetics is something that’s worked incredibly well in other MMOs out there, and even while Blizzard has dipped into that with their digital store, there’s nothing stopping them from expanding that out. The fact that TCG and super-rare-drop stuff like Ashes of A’lar can be found on the BMAH should demonstrate that Blizzard is fine with players trading currency to circumvent a long time-consuming process.
Where I draw the line, however, is buying gold. Not only are the practical problems of gross inflation a problem, but I can foresee a circumstance where the virtual currency that’s bought with gold becomes a taxable asset. As in Blizzard gets taxed by the federal government for all of the currency they’re doling out. That gets into international finance disputes, exchange rates, complicated tax code junk… and while one might counter by saying that other MMOs have sold their virtual currency without any kind of repercussions, keep in mind that no other MMO has as many players as WoW. When your game population is still greater than the individual population of most states in the Union, that becomes a very large amount of money very, very quickly.
So it’s not just a matter of how gold-selling affects economics in Azeroth; it’s got some real effects on economics in the Real as well, and that’s what keeps it from happening.