Litterbox cabinet - SUCH A GOOD IDEA! Give the cats their own little litter box cubby room. It gives them their privacy and you can contain any mess on the outside of the litter box and easily clean it up.
ceiling furniture means doesnt take up space on the floor, but then maybe you need high ceiling for it. plus not all owners will want cats jumping on them from up high and like OMG! get some yourself some pawtastic adorable cat apparel!