This is getting WAYYY out of hand now. First, people that claim that SE is thinking of going to a PLEX system, really need to show or link their evidence for this. Otherwise, it's just a matter of he said she said. If you claim something, then the burden of proof for the claim falls on your shoulders, a simple fact that when you fail to understand, you're now in the same group as the conspiracy theorists and religious idiots who claim to "know" without proof. As for me, I'm not mindless enough to support anything without proof, and further, proof exists abundantly for the argument against any system where a cash shop item is able to be sold for in game currency. I believe the best way is to take a system from a game where the system itself cuts out the middle ground by allowing players to convert cash shop currency directly to in game currency based on a conversion rate regulated by the game's very own market. Guild Wars 2's system worked on a system that allowed players to buy cash shop currency with real money and convert it to in game money, or buy the same currency with in game money. Converting cash shop currency to in game currency would yield a lower amount compared to how much it cost to buy cash shop currency with in game currency. This system was put in place in a hope to stop RMT (which it didn't) and also lower inflation (Which evidence posted below will also show it failed to do). In fact, as you can see, over the course of the game's existence, the conversion rate for Gems to gold is now 50 times what it was at the launch, and the cost to buy gems from gold is now 55 times what it was at launch. This is the simplest form of real money to in game money transaction that can be referenced. It shows a distinct link between a game's economy and the inflation caused by such a system from its implementation to the present. These prices, by the way, are based off the conversion of 100 cash shop currency to gold, and the price of 100 cash shop currency using in game gold. The price of the cash shop currency in real world money is still the same.
The rate of exchange for Guild Wars 2 can be found here http://www.gw2spidy.com/gem where in game data values are being followed and recorded
One more thing to consider is that Guild Wars 2 is a one time pay model. Meaning, you do not buy game time, you buy the game once, and you are able to play continuously. The reason I mention this is that the items sold in their cash shop are of no real necessity. Some do give slight advantages to game play, but none so much that they effect someone's ability to succeed in the game. Now, I bring up this fact because the request for a PLEX system means one thing very important, this item can be a make or break item, as instead of just small advantages that effect more of your quality of life in the game rather than the game itself. When you begin to sell any items that actually effect a game drastically (i.e. play time) then you have just turned demand for the item from want to necessity. This problem can best be illustrated by health care. The demand for health care is infinite, since every person wants to live. Turning something that is a necessity to live into a for profit business means that you can set any price you want, and so greed corrupts the very system until only the wealthy can afford to live. The same can be seen in this system. The demand for a time scroll to play will be never ending, thus the price for them can be set to whatever someone wants it to be. Of course, competition in the market will keep a weak check on prices, however, it simply won't matter as there will never be enough supply to meet this demand. So now, as a counter, the consumer who is farming and selling goods to afford their time scrolls will raise the prices on the goods they sell to make the profit they need. The goods they sell go up in price, and any items effected by such raises in prices will also go up in price, including crafted gear.
So now, imagine you're a new player to the game, no crafts, no gatherers, only a little two leaf next to your head and enough cash to afford the subscription every month/3 months/6 months. You enter a game where you could never afford to buy the armor for you level, so instead, you're relegated to farming armor from other sources (quests, leves, dungeons) but now, you want to start crafting to make the gil to afford some armor, or maybe to afford a time scoll so that you can save money and sell your own time scroll and get in on the action. That's not going to happen unless you gather items, because you simply can't afford any of the mats on the market. So you now you are forced to raise a gathering class too in order to furnish the items to craft, so that you can afford to craft items to sell or use. What was once a game where you could choose to just fight mobs and battle has now turned into Farmville for the greedy. The only light in all of this is the fact that there are things that don't require gil to buy, however, those things are at level 50 or completely useless anyways (i.e. GC gear), so now, as a new player, you have only two choices, grind your way to level 50, in crappy patch work gear since you can't afford market board prices, or grind gatherers and crafters to make your gear yourself, which takes quite a bit of time as well. Then, there's the third choice... quit and go do something else more productive, like play Farmville or something.
So again, to recap what I have said before, ruin a game's economy, then say goodbye to seeing new players. When you say goodbye to new players, then all you are left with are veterans, who whittle away one by one.
Also, to put a cap on the whole "WoW is doing it" thing. WoW is NOT doing the same thing as what is being discussed here. WoW is selling time scolls, yes. WoW is allowing players to put time scrolls up for sale on their markets, yes. However, WoW is NOT allowing players to set their prices for said Time Scrolls. The price you can sell said time scoll in WoW is set, and can not be changed by the players. Such control allows them to not just control, but eliminate the inflation that might have ensued. So STOP saying "WoW is doing it" because they aren't doing the same thing, they are doing something that's actually smart, allowing stupid players to be stupid and buy time scrolls with their own real money to make a quick, but limited in game buck. So their system IS different, and more like buying a time scoll and then vendoring it instead of exploiting other players and a free market for an item with limitless demand.