First and foremost, allow me to introduce myself as someone who avidly PvPs in MMOs. I'm a seven-time Gladiator from WoW and have already put in well into triple digits worth of games in FFXIV. Now, honestly, I don't intend for anyone to actually care about anything I've just typed but I mentioned it just to qualify myself as someone who takes PvP seriously and has a lot of experience with it.
So how would I improve PvP in FFXIV? As follows:
1) Reduce the preparation time from 2 minutes down to 1 minute.
2) Class diversity needs to be addressed. On one hand, I would remove the class restrictions of one tank, one healer, and two DPS. However, I do understand why it was implemented this way. On the other hand, I feel the introduction of more classes may alleviate this issue. I do not, however, feel it's good design for a group to be forced into taking a tank arbitrarily. I feel it should be the group's decision as to whether a tank is beneficial to them. If you are worried that tanks will not get used otherwise, then clearly you need to provide them some powerful utility to make them attractive.
3) Instant interruption to casters from direct damage needs to be toned down. As the game doesn't really rely on "interrupts" as other MMO PvP does, I understand the idea here. However, I feel there is a reasonable middle-ground one could arrive at between: damage always interrupts casting and damage never interrupts casting. Perhaps receiving three direct attacks during one spell results in an interruption? Alternatively, perhaps the CDs afforded to casters to avoid interruption could use a buff. As it stands right now, they are borderline worthless as the moment they are popped, a simple stun negates them. If you are not going to budge on this, at least increase the effectiveness of Skill and Spell Speed in PvP then so it's more reasonable to get a cast off.
4) More maps. Fighting on the same map over and over again gets boring quick. There is only so much strategy that can be developed for a given area. I would love to see a map for each of Gridania and Ul'dah similar to how you did the housing. Map diversity would keep things a bit more interesting. Please no "Ring of Valor" type maps though. For those that were unaware, this was an Arena map from WoW wherein there were environmental effects that could damage you and pillars that moved up and down.
5) You need a ladder of some sorts. Right now, I don't see any way of measuring one's self against your peers. This is exactly what drives many PvPers.
6) Get rid of "Fresh Meat". I'm not sure what the objective was behind this, but replacing everyone's name with "Fresh Meat" is really silly. It serves no purpose in my mind other than obstructing the ability to communicate effectively with your team. Instead of being able to call out a name to switch to, we must resort to memorization of all gear sets for all classes, for all four party members, and call them out by class. By the way, you forgot to remove the hiding of names from emotes. I have a macro set up that /laugh's at my target and when I do this to an opponent in the Wolves' Den, it shows me their name. What a shame to consider that my opponents believe I'm laughing at them before we've even engaged in combat. If nothing else, it serves as a reminder to them that they should employ the fool-proof "train the Black Mage 24/7/365" rule for PvP.
7) Ease the gearing curve a bit for the initial set or get rid of it. The Warwolf set is immensely overpriced. I'm into triple-digits worth of games and I've obtained a lone piece. At the pace I'm going, it will take several months to obtain this set only to see it eventually upgraded to an even pricier Direwolf set.
8) Make further improvements to server responsiveness. As it stands right now, the PvP in this game feels a bit "laggy". It's not uncommon for a cast to finish on a target long after their character has already disappeared behind a pillar.