It's entirely possible this is already covered with houses - I didn't get the chance to buy or enter one today, so I have no idea what goes on inside a house, but:
It would be great to be able to own, rent, or otherwise reserve (freely bookable) an in-game area to be invite-only for at least a period of time. The specific use case that got me thinking about this was cooperative trades: today I ran across two other players trading items in order to cook up an item together, and they had to temporarily drop some of their inventory on the ground in order to free up the space necessary to shuffle things from one person to the other. I didn't realize what was going on at first and said "ooh, spinach! don't mind if I do. Yoink!" before one of the players asked me politely to put down the loot. Were they able to make this transaction behind closed doors, they wouldn't have to worry about pesky passersby.