There are some fundamental issues with being able to purchase gil with real money through any system. It means changing some pretty substancial reward systems, most notably the crafting gear. Crafting gear is currently the best gear available the moment of a raid launch. Further, the best gear a crafter can get is also often purchasable with gil. In both cases someone would, at least for a limited amount of time, be able to get the best available gear by buying it indirectly with RMT which effectively would make FF14 dangerously close Pay-to-Win. While one solution would be simply to nerf crafted gear that is sellable, that seriously impacts the reward to time investment that crafting takes which is rather unfair to crafters.

Personally, although such a system would effectively allow me to play for free, I don't think it would be good for the game.