I don't see a problem. It would be 2 close friends doing it, not 2 strangers.

Seems like it'd be very complex. If both players took charge of their own floors, you couldn't have 1 or 4 star casinos unless built unevenly, and would the decision to upgrade have to be unanimous? If they both have control of the same floors, I can't wait for the coding and testing nightmare behind all the race conditions surrounding who has control at what time.

A great idea. Half the cost, half the profits but all the fun.