I posted this on the comments for the “Large population servers” new item on playrust.com site, but I felt that I better post it here as well.
Ultima Online had a similar house load lag issue. Their solution was to load he contents of the house when a player stepped on the threshold. A similar approach could be used here.
If the houses contents were to load only when a player gains access, you would only need to load the exterior.
Access in this sense would be a house you own, the door is opened, or the door is destroyed.