Okay, so in your world you customize your house with some nice paintings, the head of the boss you just killed, some very nice antique vanilla furniture.....then what? Really, people actually think that a house is a good idea? Seems like a huge waste of time in a game that is already a waste of time.
edit: I could go with something along the lines of guild flying ships or castles, but they would always have to be PVP flagged so the opposite faction can destroy them (or at least make them unusable until they are repaired). Good way to get rid of all the gold floating around the game.