F2P works best when implemented in the design phase, not a last ditch effort to try and bring people to your game. Since FFXIV is being designed as a "P2P update every 2-3 months" style game, you can't change it to f2p without having to significantly undergo massive changes.

Yoshi-P has stated several times that he's looked into f2p and b2p models, and they just aren't a good fit for FFXIV.