I think it would be pretty cool to have two PvP zones per faction. They would be located on the borders of each faction. So this is how it would look.
DC vs EP
DC vs AD
EP vs DC
EP vs AD
AD vs DC
AD vs EP
These zones would be chock full of espionage dailies, kill quests, Random live events, Delves, Dolmens, and to top it off a competitive PVP Dungeon it is up to you to decide whether you help your enemies defeat the greater evil or if you wish to slaughter them with the rest.
Rewards could be special mounts, gear, exp buffs, AP buffs, Alliance wide buffs, and more the possibilities are endless.
This could also be where the prisoners are located once they are incarcerated. Maybe a group of guildies can take on a quest to free you in a smaller scale 12 vs 12 prison break.
I have so many ideas its unreal these are just a few hope you like them and have some positive feedback