I haven't really thought about it and i don't know if it's been done before, as i haven't followed many contests, but how about one, where everyone is given the same main pieces of furniture and they have to use them in the room/s they decorate and furnish? Different recolors can be used and any size room, but the main pieces have to be incorporated (a couch, a bed, a vase and... a bike , for example) somehow. It would be interesting to see how people can create different things while using the same meshes and what they will add on their own.
Does that sound stupid? Or it's been done before?