The new WoW housing blogpost

[Jeeqbit]

Based on SE's perceived limits, I do not think it is feasible to have a ward for all the characters that have ever been made. Each ward is a server program. I did the maths for that a while ago and based on how many server programs they run per machine, it would require more physical space and machines than they will ever actually have. It may be easier if they used cloud servers for it and only run them if they aren't empty though.

It is definitely feasible to decouple houses from plots so that you can teleport directly inside them somehow, then make wards a reflection of active players that have logged in within 45 days. However, it is possible it would require throwing their house code away and rewriting the entire thing in a way that reuses the house data. It would require a little effort, maybe a day, or a few days, to do something like that, but they just rarely seem to touch their code at all.

Island Sanctuary is proof that they can do it, because it is effectively instanced gardens. On the technical side, it's the same thing as instanced housing. Either way, you have furnishing slots and instances are reserved upon entry, rather than remaining there when you exit like plots.