Why not just add instanced housing?

[Risvertasashi]

If the instance is only available to the owner, that stuff can be stored client side. Several things are already stored there (inventory sort, hotbars, macros) and all that would have to stay server side is a list of what furniture has been placed (but not where it was placed).

Honestly even stored server side it's not that much data, or shouldn't have to be. A single image-laden email would be far bigger than a list of items & positions and even a longer text email could easily be bigger. But, SE seems to have some very questionable architecture... :/