WOW is jumping the shark, or so the internet says. In the next PTR patch they are testing out a consumable that increases experience gained by 100% for a limited time and that consumable is purchased using real money in an online shop. Blizzard is leaping into a Pay To Win model people claim and ruining their good name. I don't buy that sort of thinking in the least.
First off, the idea that levelling up faster will wreck the game is a complete joke. Getting to maximum level isn't 'winning' in any competitive sense. Any moron with a mouse and a lot of time can click their way to maximum level regardless so it is hard to imagine it being considered some kind of important win condition to preserve. The level grind has become so long and involved (especially the last 10 levels) that maintaining it as a gateway to beginning the point in the game at which there is some modicum of challenge seems unnecessary. It wouldn't bother me at all if Blizzard just straight up sold max level characters in the store. If you want to level up and do quests, do it. If you don't, then don't. Who cares?
Second, the idea that paying to win isn't currently happening is a bit unsupportable. There are all kinds of achievements to collect things and many of those things rely on outside purchases. Not just that but there are a lot of achievements that are made massively easier with access to a lot of gold and buying gold from third parties and then using it to get stuff done is a constant thing. Granted Blizzard doesn't control that but WOW is definitely not a game that is free from the power of real world cash. You can get things done if you have money to burn and nothing can stop that.
The really critical point is when the best possible gear at any given time is purchased directly from Blizzard. If the most skill intensive activities like raiding and PVPing don't award the best gear then people will rightly start bawling. At the moment you can easily get the same gear as other people using cash but you have to wait until the gear is way behind the curve; the most skilled players definitely retain their status symbols. There is no way Blizzard is going to change that because although they do bone it up on occasion they aren't THAT stupid. The best stuff, the most prestigious and current rewards, are always going to be gotten by playing superbly.
It looks to me like Blizzard is really aiming to let people pay to avoid the grind. If you really object to people being able to pay in money instead of time for a truly trivial task then it is time to suck it up. That is the model everyone is shifting to and Blizzard isn't going to be left out.