The current housing wards isn't the problem IMO.
The issues I see currently are as follows.
Housing costs have not been adjusted at all since housing was added. As such getting the gil for even a large plot can be trivial to a very large amount if not majority of players in the game. Leveled retainers on quick explorations can sometimes return with items that sell on the marketboard for more than the cost of a small plot. Because of this too many people can now afford a house and many wont take a small plot unless it's the only thing available. The bloated economy of the game is a result of having the rate of gil creation by players via quests/duties/vendoring items grow while offering nearly nothing in terms of gil sinks that take that gil out of circulation. The game actually does have instanced housing to a certain degree in the way of apartments and FC rooms, however because people can easily afford bigger and better they don't want what is already offered.
They have been tweaking various things over time to fight against individuals hoarding multiple plots and RMT. If they do plan to open an area in Ishgard as housing I feel like they should have it work off a new system that involves player crafting as it would be a change from who can log in and click faster and also tie in with the restoration theme. They could do that instanced or do wards.
IMO should they choose to add instanced housing however. I feel it should specifically be in the sea of clouds. From a setting prospective a house isolated all on its own fits perfectly in that area since it could be placed on its own little floating rock in the sky. Leave the neighborhood style existing wards as they are. Just keep in mind your instanced house isn't going to have its own personal marketboard.