One of the strange things about Monopoly (at least in today's world) is that once you buy a property, you no longer have to pay for it anymore. And you get paid when one of the other players lands on it, which I suppose represents "rent." But there are only so many players to "rent" all the properties on the board.

Instead, what if the renters weren't player-controlled characters? You'd have a bunch of non-player-characters that move from place to place (maybe even depending on what you charge for rent), but you also have to pay each turn for rent and upkeep whether anyone is renting there or not.

And there should also be some way of simulating the ups and downs of the housing market.

Almost none. Maybe the paper money.

Jonathan