To facilitate player-driven content, and help people learn PvP concepts, it would be very useful if there was the opposite of a free city in the campaign. A place where by default, everyone is hostile to each other, unless grouped. The same as a PvP enabled EK, this would allow guilds to fight each other, or spar against guilds of the other faction.
Reasons for this over an EK
1) Campaign world characters are now locked and would need to burn imports and exports to join an EK
2) EKs are set to 12 player limits, which wouldn't allow for larger scale battles
3) We're in pre-alpha s