There are many empty things in the Spiral but i have a couple of ideas.
1. Wizard City - Have Sir Reginald Baxby give a level 60 only quests that give pets, mounts and statues that send you to empty towers and houses in Wizard City and a new area that connects to the Haunted Cave that gate which is another cave where there are a lot ghosts and these arent like the rest of WC thses will be rank 9 regular to rank 10 elite and there are five bosses three of them rank 9 and two of them rank 10 plus it connects to a dungeon which is harder than the Great Spyre and Kensington Park where there are two bosses the first has 7,500 hp and the last boss has 15,000 hp when you kill him you get two pets a a mount and two statues also they drop pets and level 60 only items plus permanent mounts and other crowns items. 2. Krokotopia - Those of you wo have completed Briskbreeze Tower know that when you defeat the last boss he drops a key to a tower to Krokotopia so there can be a tower anywhere in KT that is just like Briskbreeze Tower. 3. Marleybone - In Marleybone KI can add something to Barkingham Palace, a quest that you must have done DS to get and is given by the queen that area would be an interior so it would be a palace and in the dungeons of the Palace are mini instances that have some of the bosses of MB but bigger then the last one has Meowiarty.