The Warcraft token system works where you buy the token for real money and sell it on the market board. Thus "buying" gil.

The buyer ingame then redeems it for a months sub or the equivilant of crysta, thus buying a sub or cash shop items with gil.

The important part of this type of system is that gil is never generated, it merely passes from one player to another. Thus inflation doesn't really happen.

The advantages of course are RMT does indeed decline drastically (why buy gil illegally and risk a ban when a safe legal alternative is available) and cash shop items are no longer cash only if you have the gil. Gil becomes more useful. Enix also makes a lot of profit, since the token might cost, say $20 and redeem for $14 crysta. So it's win-win. To be fair, it's a much better idea than shoving features behind premium paywalls in a subscription game.