To be honest it is really too early to talk about this kind of things. The fact remains that the game will launch as a P2P. We have a long way until we see if the game is gonna go F2P.
With that been said, if the game in fact go with a F2P model what remains is what kind of F2P will it be.
Even if it goes F2P i want it to have a subscription fee that has everything without me having to pay for this and that. Something like Age of Conan did if i am not mistaken?
In general though, if the game is good well balanced and people like it, P2P is more than enough to give good profit to SE.
And lets not forget that if SE cares for the game and the FF games at general they should try to keep it at its best shape and not go for the easy way out with a F2P model. I understand that profit is what matters but that is also how you lose fans.
Thats my 2 cents in the matter.