Not sure why the ability to make changes should be time limited, or how that would have any negative impact on game play.
I do agree that a barbershop should be implemented (doubly so if there are plans to add previously unavailable options), and that accessing its services should cost gil, NOT real currency.
Race changes I would even say should be handled with in game currency. Granted its accepted that such a drastic cosmetic change cost IRL money, but its barely any different from changing your hairstyle or model height from the stand point of the system. (Granted, I'm not for race changes. We have multiple character slots for a reason, even if they for some odd ball reason charge us more for each slot)
The only games I know of which charge for cosmetic changes to the character model (aside from race changes) are of the 'free to play' variety. The kind of game who's business model revolves around generating the need for these chages by strictly limiting character options, and offering premium choices with the incentive of individualizing your avatar from the sea of repetitious faces. If I am paying a monthly fee for a game, I expect any services of a 'cosmetic nature' added to the game be included in this fee. Its part of the game I am playing, that I paid for up front and continue to pay for to fund its maintenance and future development. Everyone who plays such games should be afforded these options as such.
Granted, in the case of FFXIV there is a chance it could transition to a free to play like many recent MMOs have. If such a thing should happen, I would expect at the least that current players who purchased the game be given 'premium access' considering that we already paid the for the regular or collectors edition of the game.