Over the holidays, Blizzard floated the idea of introducing an item which can be used to give a month's subscription, and allow that item to be sold in-game. Essentially taking Eve Online's PLEX and applying it to WoW.
I think this is a bad idea.
I think this is similar to Diablo 3's Auction House. There the problem was with third-party trading, and Blizzard introduced the AH to combat scams. That worked, but ended up warping the game even farther. WoW PLEX would be similar. It would be introduced to combat Real Money Transfers from sketchy sites. But it does this by turning players into RMTers, by warping their incentives.
You can see this in Eve Online. Eve has a significant problem with scamming, lotteries, multiboxing and similar shenanigans. I believe this is because PLEX helps incentivize these actions, not just among the illegal third parties, but for regular players.
A lot of Eve partisans will say that PLEX has been good for Eve. Truthfully, I am not so sure. I think PLEX has masked a lot of problems with Eve, especially on the resource production side. Problems which would have been exposed and fixed a lot earlier without the bandaid of PLEX.
As well, I don't believe that it is good for the game to have one segment of stronger players play for free at the expense of other weaker players. Right now, the playing field is relatively equal. WoW rests on a broad base of subscribers, and we are all relatively equal. The necessary monetary support is divorced from the in-game universe.
PLEX for WoW is a bad idea. It warps the incentives for a significant fraction of the playerbase, and creates a real divide between those players who free-ride, and those who pay. I urge Blizzard to reject this idea.
Edit: I posted this in the comments. Hopefully it makes the parallel with D3 and WoW more clear.
D2 had a problem with scammers. D3 introduced a mechanic (the Auction House) to combat that problem. That mechanic warped the incentives for the larger playerbase. The cure was worse than the disease.
WoW has a problem with 3rd party RMT. WoW is proposing to introduce a mechanic (WoW PLEX) to combat that problem. That mechanic will warp the incentives for the larger playerbase. The cure will be worse than the disease.