Medicare already has a voucher program. It is called Medicare Advantage and it failed.
"the market-based arm of the program costs more, not less, per beneficiary. Those fixed monthly payments to Advantage plans are, on average, 13 percent above fee-for-service Medicare costs. It didn’t start out that way. Originally, private Medicare plans were paid 95 percent of per beneficiary fee-for-service costs. The logic was that private plans ought to be able to provide Medicare services more efficiently than traditional Medicare through a combination of controlling utilization and driving hard bargains with providers. So, Medicare used to take five percent off the top.
Then Congress began to ratchet up payments, first with the 1997 Balanced Budget Act and more recently with the 2003 Medicare Modernization Act. (This year’s health reform law aims to reduce Advantage payments, though still not below 100 percent of fee-for-service costs on average.) Ironically, traditional Medicare payment regulatory reforms–like the prospective payment of hospitals and home health agencies–have been more successful (even if not anywhere near successful enough) in mollifying the rate of growth in the program’s costs.
What’s going on? Why is the market-based Advantage voucher system not helping to control Medicare costs? The answer is that health care cost control is tough, technicallyand politically. Provider groups typically resist it. When it pertains to Medicare, beneficiaries resist it too. By adding another private-sector layer to the program–health insurers–the Advantage program invites a third source of political pressure. Rent-seeking by providers and insurers, as well as the power of the beneficiary constituency, align in their encouragement of higher Advantage payments. Congress, apparently, is willing to yield to that encouragement."
http://theincidentaleconomist.com/wordpress/for-cost-control-vouchers-and-medicare-dont-add-up/