While I generally agree with everyone calling for more placement slots, I'd be actually super satisfied and happy with more STORAGE slots. There are so many gorgeous aesthetics and experiments to be done with indoor and outdoor decoration, particularly with all those designs which only use one floor, and I'd love to have different options, but unless the decor overlaps in some way, I'd only have enough storage for two "looks" (say, a Hingan/Japanese look and a modern beachfront villa look) and if I want to experiment within them, or have a third look (e.g. old world library), I've got nowhere to put all the extra furniture.
Also, related to the above, an in-game first-party glamour plate system for houses/apartments would be SO nice.
(I'm sure various other people brought these up, of course, but just adding my +1 :P )