Quick suggestion...

[Syrehn]

Even if they add instanced housing it still uses server resources. The current limitations on housing, according to SE, are related to server resources which probably also factors in the costs associated with it.

So regardless of if they add more wards or add instanced housing they're still going to have to allocate more server resources; which is something they are attempting to do in phases with the existing housing structure instead of building an instance system. Again, this is likely tied to demand and infrastructure cost.

Mind you they have mentioned that when they release new wards there might be an apartment style complex coming with it so that's probably as close to instanced housing as you'll get.