First of all, it makes no sense if you've mandated the specifications of the product being sold via legislation. Having said that, a huge benefit would be the ability to buy insurance: actual insurance, in which you're paying a subscription fee for the service of protecting you from the risk of a huge surgery bill, rather than a payment plan that covers everything inside the walls of a hospital. As a young adult, I would be happy to pay for a service that would insulate me from risk I can't handle, because it would make me financially stable. But if the plan also covers predictable things like obese people needing diabetes meds, children being delivered, and obscenely expensive cancer treatment that only slightly extends a low-quality end of life, that's a different question. Suddenly (probability of medical emergency) X (expected cost) << (cost of insurance premium), even if you add a $500 penalty to the left side of the equation. Bankruptcy seems like the smart insurance if I'm not amassing significant savings, in that case.
Everything outside of those complicated, expensive procedures would suddenly be susceptible to price sensitivity, since the users would also be the people paying. Faced with that pressure, routine procedures would fall to prices that don't look like typos.
Having said that, what I've read about the British system seems like it could be effective, if it were politically feasible: procedures have to stay below the cost per unit of increase in life expectancy or quality of life, or else you have to fund it yourself. When the current American system was being battled into law, it seems like that number was about 30kpounds per year of life.