What is the objective? To increase subscribers by allowing a modified FTP model? or to combat RMT?

If the former, then yes I would agree that this could probably help, but right now whether or not the game needs the help is unknown, so seems premature to me.

If the later, "legalizing" the purchasing of gil would certainly increase the number of people to buy gil (obviously). Legalization is, at times, a response to a belief that the costs of prevention are outweighed by the problem. Here, the costs of prevention are predominantly absorbed by SE. They expend X amount to combat RMT, and while one can argue that those resources take away from development, I think that's a pretty flimsy argument. The cost to players of RMT is really if/when RMT is destroying some aspect of gameplay by monopolizing something. Again, not sure right now we are facing this issue.

So seems like adding this system would possible damage unofficial RMT, but at the expense of increasing RMT overall. I don't think we are facing a situation where unofficial gil selling is so rampant that we need to legalize in order to better control/tax the system. Looking at IGE, for example, prices for gil are such that it would seem nobody in their right mind would be buying ($13 for 1300 gil). Are we really facing some major unofficial gil selling issue that we need to legalize and increase RMT?