For the record: I hate battlegrounds. Now, I'm not talking about rated battlegrounds: Those require you to put together a team and be social. No, I'm talking about jumping into a random group with people you never met and expect to pull off a victory despite having no real reason to even talk to them.
PvP is a very dynamic type of gameplay to begin with. You must be able to recognize various situations and adapt, be able to use a wide variety of your abilities as well as knowing your opponents, and in goal oriented scenarios know when and where to attack and retreat. Quick reflexes is a good part of it, of course, but they are hardly everything if you haven't a clue where to aim yourself.
It goes without saying that an MMO that is based on PvP should have these qualities in mind, and use the idea of a persistent world to cater to the type of battles that are memorable. Territories to be captured, buildings to be destroyed and resources to use against your enemy. Rewards that matter and can turn the tide against your enemy. This kind of dynamic virtual warfare is perfect for the PvP oriented player.
Of course, then we come to the dreaded word that destroys a good number of great ideas: Balance. How would you balance that type of gameplay? If one faction has more people, suddenly the game needs to be able to compensate that. And since it is a dynamic battle you cannot account for the amount of players in one given area at any time. How do you integrate gear into those battles as well? People at lower gear levels would be mowed down, and that isn't fun at all. The list of problems goes on and on.
And unfortunately, the battleground does not have those issues. It keeps players at the same level range, evens the playing field and creates areas that are tactically fair to both sides. And I hate it. It's a sterilized answer, one that chooses to omit problems rather than resolve them. If Horde has more people on a server than Alliance, it doesn't matter because the battle will not change anything in the game world. You get your points, and then you get to do the same thing over again. These vacuum packed battles are meaningless.
Prime, here's looking at you. Let's hope you can create an experience that doesn't have to resort to battlegrounds to captivate the dedicated PvP audience.