Personally, the old TS1/TS2 idea of assigning a lot as either "residential" or "community" made multi-purpose lots much simpler. Lot "traits" so to speak were defined by the objects placed within them, and those objects each had their corresponding NPCs. Now in TS4, a body can have a designated nightclub building on a lot, but if the lot trait is "restaurant", no one will be dancing there, regardless of hiring a DJ NPC.
I am cautiously hopeful of something like this or a multi-trait lot in the future, because TS4 has seen revamps in aspirations, careers, and even gameplay interfaces. (ie. town maps) Could even pose as a solution to the dreaded culling. Until then, I guess I'll read. :)