Not sure if I understand your post correctly but we already have that.

Both Bit-X and Xapo's cards are backed by bitcoin meaning that you do not have to convert your bitcoin to fiat and then transfer the fiat to the card. Their cards are directly linked to your wallet and when you make a transaction they take the bitcoin equivalent from your wallet to pay for the transaction. So you are actually paying in bitcoin but they convert it then for the vendor and pays him (or the payment processor) in fiat.

Also, with Bit-X you can even use Litecoin (think other alt coins as well). From my understanding they will take from your btc wallet but if there is not enough but you do have enough ltc in your ltc wallet then they will pay the transaction from there. Best to check their site, I'm sure I saw it on there somewhere but stand to be corrected if need be.