I was so excited about this thread I got a forum account to reply.. heh.
Here's what I'm thinking:
No locks. No racks. When you're online, you get a prompt if someone wants to get in your house and you can say yes or no. When you're offline, since no one will want to store their things in an unlockable house anyway, people can come and go but since it's cosmetic and doesn't have real items in it unless you're very (VERY) trusting, there's no need to be worried something will be changed, ruined or stolen. (Although I saw what you posted, Merlac, and I really like the idea. Like, when you log out, your items left on the floor disappear or something).
Also, if someone comes in your house while you're offline and then you come online and want them out, you can kick them. People could have a notification or something when they come in like "<name1> and <name2> are currently in your house".
They could hook up the party planning system to offer to host the party at your house if you have one!
The original buyer of the house can add people as "housemates", so they can share the house with others. They all are equal, except the buyer is the one that can edit everything (remove housemates and the like). People can add, change, etc. their own things/rooms/whatever, but only the buyer is the one with the full control, because they bought the house. People can make things like room descriptions, "items" (not usable ones, but ones seen around the room and such). Housemates and the buyer all kick someone from their house if they do not want the person in at the time. The buyer and housemates cannot be kicked out of the house.
In regards to where the houses could be, maybe one person can own one house in the whole game, and can choose what area of Genesis it's put in? And for flexibility, people could sell or transfer ownership of their house to someone else. (Maybe even just move the house they have if they really wanted to keep it that much?)
I don't know. This might seem too complex to some people. Just my thoughts. I think this is a GREAT roleplay opportunity. I have seen a fair amount of MUDs with house systems that don't have much (if any) problems at all, and in fact just having that option available enriches the roleplaying experience for their players. I really support the idea in general.
There are three types of people: those who can count, and those who can't.