I can point out one HUGE problem with studios owning theaters, Securities Fraud.
Right now, theaters get none of the box office revenue for the first two weekends. That horrible deal allows studios to buy up tickets to inflate the performance of certain movies. So, a massive flop can be converted into a modest success thereby affecting the stock price of the parent company. Hollywood accounting is already extremely corrupt, this would take it to a whole new level.
While movie studios do buy their own tickets, it is absolutely not true that theaters take no revenue for the first few weeks. They take a smaller portion at the beginning and as the movie stays in longer, that portion goes up. It usually works out to ~50% in the end. If they received nothing for the first two weekends, theaters would be out of business by now.