Between Ryan and Krugman we have two extremes. Ryan wants to throw folks on the market, even folks who may have been paying into Medicare for 40+ years, yes I stated working at 12 and paid SSI at 14! Child labor, no, NYC gave work permits to deliver newspapers and somehow at 14 I worked in an HMO in NY as an assistant to a group of physicians. Could never do that now but that is another story.
Back to Ryan, if I were 15 years or more younger then I would get Ryan Care, namely a check for something at some age most likely letter than 65 and told go fish, namely find an insurer. Krugman is spot on this time, try and find a policy. I can get auto insurance pretty simply because I have been doing it for more than half a century. It was also around before that. But old age health insurance, the frauds will be explosive, it will make the banking collapse look like Sunday School efforts. It just will not work and no matter how you try to fix it ab initio there will be a plethora of unintended consequences, just watch the current health care plan.
On the other hand the current Health Care Plan has the same problems, ACO, IFAB, etc etc, it just goes on. Government employees on top of Government employees, it will be the land of zombies.
Somewhere there must be a middle ground. I have made several detailed suggestions but no one in DC seems to even try such an approach. Pity.