Ask HN: Bitcoin-backed fractional reserve currency

"Easier to buy and use than Bitcoin, guaranteed secure, and exchangeable at any time 1:1 to BTC or cash equivalent. Buy with your credit card."

Could something like this work? People would probably be content with the increased convenience, and it could substantially increase the amount of people that use Bitcoins, theoretically even higher than the amount of Bitcoins that actually exist. It could make money through exchange fees like an exchange does now, and it could be faster and function with a fractional BTC reserve.