It's already possible to have a credit card-like service combined with Bitcoin. It's called a Bitcoin debit card -- you deposit BTC, and you'll then get the ability to pay basically everywhere in the world. If you have no more coins left, you can't buy anything. It's not based on debt as is the case with credit cards. Major benefit. If you're seriously interested in it, then look for services as BitPay, Xapo, Bit-X. They all offer Bitcoin related debit cards.