One other problem is if you are in a subspecialty, there are some issues with private practice without insurance network access:
1. Unless you are in a practice area that already is not covered by insurance and naturally has a patient pay direct model (cosmetics, some dermatology, neurology "pain control"), you will need referrals as direct to patient advertising is difficult, and what primary care provider would refer to a non ABMS physician when they could easily refer them to one?
2. Malpractice insurance and supervision would be extremely onerous.
3. Good luck even in rural areas on getting institutional access to practice. Most are limiting this, even for ER which used to have a large number of non-certified providers.