So currently we have the city sieges in Empire made up of public quests, so after all the open realm versus realm play to capture the city you end up in the games PvE mechanic.
I imagine Mythic would not want all their hard effort wasted and thrown away. But we also still have two city pairings left to come. To vary the end game as well as Land of the Dead the next two cites follow a different mechanic in their capture.
How about creating the Elf pairing cities based on a scenario city siege mechanic?
Break the city into lots of smaller instance scenarios which tell the tale of a city siege. You start at the outer scenario maybe based on the battlements then work you way through a string of scenarios which take you through houses, palace grounds to the throne room. Fail on one scenario, maybe you have to redo it or it moves you back down the chain.
Use the scenario types (capture the flag, objective control…) in the tale here are a few ideas:
Objective control of scenario situated on city battlements. The scenario had various control objectives like gate house and anti siege weaponry.
Scenario based in the nobles houses of the city which have magical wards which protect the inner city. Like the ‘Stone Troll Crossing’ you have to take a crystal and run through each of the houses placing the crystal on each ward to disable the barrier. The action would be very close quarters, maybe you could have the ability to use ranged ability through windows of the houses.
After reading Malus Darkblade novels describing the city Naggarond the complex streets and towers would lend themselves to an excellent range of scenarios.