It took Medicare 6 years to reach the enrollment numbers we saw in Obamacare this year. And, next year, Obamacare will have more enrollees than Medicare had in its 10th year.
Medicare now covers just over 50 million Americans after 50 years in existence. It will take Obamacare a fraction of that time.
The majority of Obamacare numbers are due to the expansion of Medicaid (which underscores my point about the significance of the Social Security Amendments of 1965).
The ACA is a huge first step in much needed reshaping of our nations healthcare system, but a significant portion of the heavy lifting has accomplished to date are built on the aforementioned legislation.
Something tells me that if Republicans own in 2016 or 2020 they would appoint people to the Medicare board who would suddenly see things differently, and see that as an excuse to roll back not only Obamacare but Medicare itself.