Ezra Klein envisions it:
I think that path would look something like this: With health-care reform either repealed or overturned, both Democrats and Republicans shy away from proposing any big changes to the health-care system for the next decade or so. But with continued increases in the cost of health insurance and a steady erosion in employer-based coverage, Democrats begin dipping their toes in the water with a strategy based around incremental expansions of Medicare, Medicaid, and the Children’s Health Insurance Program.
They move these policies through budget reconciliation, where they can be passed with 51 votes in the Senate, and, over time, this leads to more and more Americans being covered through public insurance. Eventually, we end up with something close to a single-payer system, as a majority of Americans — and particularly a majority of Americans who have significant health risks — are covered by the government.
But Klein doesn't welcome this scenario because "it’s not at all obvious it would be a good system, and, in the decades between here and there, there will be a lot of unnecessary suffering and deaths among the uninsured." I shared my thoughts on Obamacare and single-payer last night.
The Dish 