It already exists in the game !!
An instanced Southsun map, pretty much as it is, would be incredible for GvG or a large scale PvP fights between servers.
The thought occurred to me how much fun this would be during a match of Southsun Survival the other day. Not much would have to be changed on the map at all, just add some WvWvW elements and let two guilds or two servers fight one another on the Southsun map.
karkas optional!
The only thing necessary for the triumph of evil is for good men to do nothing – Edmund Burke