Medicare Advantage itself seems to be in no danger of disappearing. In fact, the ranks of members are growing, and at this point one-quarter of Medicare enrollees are signed onto it, according to several sources. What is under scrutiny and might be changed is how MA is subsidized.

Medicare Advantage was born out of the Balanced Budget Act of 1997 as another option to "traditional" or "original" Medicare. Original Medicare offered separately Part A (which covers hospital costs) and Part B (which covers doctor visits and treatments). Medicare Advantage originally called Medicare Part C or Medicare+, offers both parts as well as Part D drug coverage, which was enacted in 2001.

Original Medicare allows enrollees to visit any doctor anywhere (that doctors take Medicare), while Medicare Advantage requires enrollees to sign on with a private insurance company such as Blue Cross Blue Shield and Humana, and use the doctors and hospitals in its network. To entice enrollees, MA plans offer extras like gym memberships and eyeglass coverage and in some cases, extra drug coverage.

The government pays Original Medicare doctors and hospitals on a fee for service basis, by subsidizing doctors or hospitals for specific procedures. This is far more transparent than what Medicare Advantage plans, which bill the government on the basis of each members health known as a risk score. Several sources investigating this form of coding have raised questions about whether MA insurers aren't boosting those scores by creating unnecessary diagnoses and tests.

According to a March 2013 report by Medpac (which provides research to Congress), "For MA, the commission recommended that payments be brought down from previous high levels and that they be set so that the payment system is neutral and does not favor either MA or the traditional FFE program."

The overpayment to MA could be anywhere from $3.2 million to $5.1 billion over the past two years, according to Government Accounting Office

In a January 2013 report on MA, it says: "To help ensure appropriate payments to MA plans, we recommended that CMS take steps to improve the accuracy of the adjustment made for differences in diagnostic coding practices between MA plans and Medicare FFS."

The CMS indicates it's moving in the direction of merging the two forms of payments so MA pay would be more in line with fee for service.

Either way, there's no simple fix for MA or Medicare itself, says Marlene Lund, an insurance provider in Omaha, Neb.

"They're looking to slowing weed it out just like they are with Medicare," she says. "Years ago, you got on Medicare and would have great coverage. But it's hard to plan retirement with so many unknown rules. We'll see more and more doctors who won't accept Medicare and they're looking to increase Medicaid."

In short, for the moment what will happen in 2014 is anybody's guess.