That depends on a few factors for me.
Personally, I don't want open world PVP. I also feel that few people think of FFXIV when they think of PvP. While it might attract some players, I doubt it would attract many.
That said, if they were to add it, I'd want to make sure that there are PvE servers and PvP servers. I mean true PvE servers, not where you get flagged for PvP if you enter certain areas. Not where you get cross-realm transferred (not a thing here but it could be?) to a PvP realm and die trying to do your quest. I am a PvE player and all the PvP deaths I've had in WoW have been truly aggravating. I would not like to see that here.
Again, I'm fine if they add PvP servers though. I doubt that it would be very popular here.