Diablo III.
They tried to get rid of the obnoxious RMT which exist in Diablo II by introducing a real-money market board.
Has everyone now knows, it was a huge failure, because making it legit' drove people in way more than expected. Players were actually playing "Marketboard: The Game - Featuring a bit of Diablo lore".
You can't compare the practice of buying RMT gold by breaking the rules (and taking the risk of seeing your account banned), to a legitimate way of purchasing the game currency, designed by the developper themselves. Far less people are actually buying gold from RMT than if it was legalized.
The scale is just not the same at all.
I'm pretty sure that you know what Pay to Win stand for, and that is related to getting ingame advantages by using real world currency.
All the examples you provided are only purchased with the currency of the game. And there is nothing wrong with that.
But buying these with real world money? Yeah, there is a problem. Inequalities, blablabla, I already spoke about it.
As I said, the scale of RMT affecting the economy cannot be compared to the effects a legit system like PLEX would have.
The inflation people are speaking about comes down to the fact that, if you equalize the economy by giving each player a chance to grab some gils from another rich one, then, that first player has absolutly no reason to try and craft or gather material to fill the marketboard, trying to make some gils, since an easier and legitimate way will be available.
Therefore, the demand will completly crush the supply in no time, and the prices will rise like crazy... making the "paying real money for gils" thing even more mandatory.
In fact, the main source of supply will probably come from bots. They will make a ton of money, because they will be doing a job that nobody wants to do anymore. They even would be able to pay their subscription only by the gils they are making, thus, making hell-a-lot cheaper to run a bot... even if it get banned by SE.
The inflation problem is a real concern with more effect than most people in this thread think it will.
So, a new player who could pay real money to skip this "boring leveling" should be able to, but if another new player doesn't quite have the money to do so, he'll just be sitting behind?
Even if you look only at the "new player benefits" from that kind of system, you are already creating inequalities.
Plus, this particular point doesn't apply to FFXIV yet. The content is not "years" old, and we have yet to see how SE will handle new players in Heavensward. What we can tell is they are really trying to keep "old content" alive, would it be with roulettes or the relic quest.
Nobody will learn how to craft 1-4 stars stuff by leveling their crafting classes... hell, they can't even do that at 50 before having all classes at 50. Anyway, you are assuming that "learning how to craft" cannot be done if you go straight to 50. Well, that's not true, you can and you will.
Also, again, inequalities. If you have to spend tons of gils to do your leves, to buy your own gear and sell stuff on the market board in order to level up, and another player comes in, takes his credit card and skip all of this, you'll probably make the first player a bit angry/jealous with that system. He will then have the choice of continuing the way he started... or buy a wonderful bag of gils to skyrocket his classes like mister credit card.
WoW really cannot be compared to anything in that regard. Plus, they are losing subs like crazy.
The only way they keep surviving, is by welcoming people back with stuff like character boosts.
The state of FFXIV and the state of WoW are completly different.
You were speaking about "years old content"... well, FFXIV doesn't have that yet. We don't even have the first expension.
It's not because "it worked on WoW" that it will work everywhere else.
Taking the context of FFXIV itself would be a better way to argue about that.