Nobody knows. You couldn't have Medicare as we know it for everyone. Theoretically specialists would be busier in terms of volume while per patient reimbursement would drop for most. Realistically you couldn't have 300 million + people with $183 deductibles and no restrictions on specialist visits, imaging studies, procedures, etc. Meaning how often patients can come see a podiatrist and what services medicare would cover would likely need to be cut further. I actually don't mind Medicare patients. In Medicare's defense they set rules and if you follow them you know exactly what is and is not covered and exactly what you're going to get paid. There is no automatic denial of all 25 modifiers like BCBS recently implemented. There are few, if any, peer to peers, prior authorizations, pre certs, etc. IMO Medicare is "easy." The problem is that with Medicare for everyone comes more CMS oversight/regulatory burdens. CMS is leading the charge in terms of making a physician's ability to run a business harder. CMS is increasing your overhead and making you spend more time doing things that have nothing to do with patient care. Any doctor who wants to give CMS more power is insane.
It would probably eviscerate the profitability of most medical fields, excluding mid levels. The government would have a monopoly on reimbursements and could name whatever price they wanted. More likely, they would cap reimbursements and give mid levels greater autonomy to cover for the artificial shortages. In other developed countries, physicians only make like 80-100k unless their patients are the wealthy. Regardless, it PROBABLY won’t happen, despite lip service by certain politicians. Big Pharma and insurance companies are worth hundreds of billions of dollars and Citizens United isn’t going anywhere.