I will PvP if I am bored or waiting for events to start with the ls and have absolutely nothing else to do.
I guess I will more if they force me to... aka have a good pve item in pvp for some reason.
I play FF mmos for the Solid PvE aspect of the game, building a guild(ls), and working together. Unless SE just blows me out of the water with PvP I see no reason to play PvP in this game over say GW2 or other Non-mmo pvp based games like starcraft and call of duty which are built around the pvp model.
If they have large scale pvp I will probably do it with my ls some... but considering the tendency of large scale pvp to fail (aion and what not) I am not holding my breath on them having true large scale pvp. Expecting more 4-12 man pvp things like in other mmos which do not interest me at all.
One thing I do want to note: SE needs to not modify anything for PvP... the PvE needs to be the main focus... I do not want class nerfs, ability nerfs, ect because 1 class slaughters ppl in PvP. They need to make 2 different ability rule sets 1 for PvE and 1 for PvP.