2. Instanced Housing
So many people just don't get it. There is an instance server. It governs all the current housing interiors, probably each of the housing wards, every apartment interior, every dungeon, raid, trial, the Firmament's DoL gathering area, the Ocean fishing boats, and any other case of something that is instanced, is run on these servers.
You think you can add the stress of thousands and thousands of housing interiors onto this without crashing the entire game?
Everyone keeps screaming instanced housing, without realizing just what it would take to deliver that. They'd need to add new servers for every world, just to handle the strain, and that means sub prices would go up to cover it all.