Something to consider.

Doctors need insurance against medical malpractice and other forms of liability. So the insurance companies would develop their own form of standardization/credentialing, much like what happens in other industries like construction or shipping, to determine what are actually the highest risk factors for liability and other losses. You wouldn't be able to get insurance without following these guidelines.

The advantage of this system is that it's not written into law, making it much, much easier for it to change and evolve over time. Insurers would compete for business by pushing up against the minimum allowable standards and innovation would occur.

The thing I think people forget, is that legislated mandates are by their very nature, extremely hard to change. Regulations of the sort the FCC uses are easier, as they can be done by the agency itself, but they have their own problems.

I just don't think it requires MD-level training to do everything we need doctors to do today. Nurse practitioners and other less-credentialed peers are already taking up a lot of workload in medical offices and costs are still exploding.

But the question that is being discussed here is not that question.