That would be fun to have. Perhaps as a safety net they could let you purchase an "apartment" when those are released and then tether that to estates you have tenant/FC access to. If something happens to the FC or the house you're a tenant of, your room is just unhooked from the estate, still accessible from the mansion/apartment building thing and there's no loss of 300k gil or obliterated on removal furniture.
I'd also like the door to the private rooms to be moveable.
