As someone who loves pvp and loves final fantasy the whole franchise, I would like to give idea's on how you can make a fun addition to the game and not forced or feel forced upon people who don't enjoy pvp.
1. If world pvp is going to be added, please make a couple new servers/realms and do not convert any of the existing into pvp.
2. Lets keep "pvp gear" out of the game please, farming pvp sets is probably the most pointless thing any game can create. Not only that it causes a lot of drama when PvP gear is being used in PvE! We would prefer you to spend the money on something productive than making junk gear who most of the people will junk in days if its tier sets. It also takes away from being unique! We don't want to look and have the same stats as the other Gladiator next to us! Not only that but it gives the PvE community players a chance to actually compete and stand a chance. Trust me if you create pvp sets someone who has top PvE gear will not stand a chance against people fully geared in pvp gear that are skilled. Having PvP/PvE gear makes it too easy for hardcore PvPers to identify the players and will focus target anyone in PvE gear! The greatest thing I personally enjoyed in FFXI is killing end game to get better gear and compete (own it up :P) in ballista. Gave me the chance to enjoy and experience the whole game as well!
3. Please skill > gear! In FFXI it didn't matter if you had a relic, if you sucked you sucked and that's what I loved about it! The balance of FFXI was amazing, yes some classes/jobs had temporary advantages but they never lasted long.
4. Rewards extremely hard to obtain. Weather it be a tunic or a weapon (most preferably a weapon) the hardcore PvP community, like the hardcore PvE community, like things that set them some what apart from the crowd with items that show how they worked hard for something. As an example: Archer PvE Relic 100dmg 50agi. PvP Relic 95dmg 50eva. or 95-100dmg (plus 50agi to players only or in player vs player environments)
I'm going to close with saying again that PLEASE DON'T FORCE THIS ON PVE'ERS!!! We don't take pride in killing someone who isn't interested or trying. Save yourselves the QQ's! Thanks for your time, feel free to leave your comments and opinions.