Good idea. It would help server load for those with multiple alts. Not that one player with 10 alts would be in all ten houses at the same time, but the convenience of streamlining them all into one instance that's shared is highly beneficial.

In regards to spouses / gf or bf, I think you should be able to grant access to your house as a joint ownership to someone, however this could be a problem for those who start relationships and break up soon after.