Before anyone jumps on me , i would just like to mention :

Right now we have a time unlimited trial ......
With level jump potions and free teleport scrolls already in the game. It does not take that much imagination to see items for sale that would unlock the trial limitations .
(yes , a sub would do that , i know )

So the mechanics are pretty much there already for it going FTP.

I would guess they would go buy to play first though.