The basic idea is that only free companies would be allowed to own the outdoors of houses (perhaps keeping the privilege for monthly gil fee - upkeep cost is the best defense against shells imo) while the indoors would be instanced allowing multiple solo players to own and edit their own personal instances similarly to FC rooms, but at larger scale and without the requirement of being part of FC. This would make it possible to stash multiple players in one plot, while creating communal places for social interactions outside, greatly improving the feeling of neighbourhood.
Example: Instead of having a street of 4 personal houses, there would be a street of 4 FC houses, each hosting instances for 10 solo players. The traffic then being increased from 4 ppl to 4 FCs + 40 random individuals.