This sounds like a good idea and a logical step forward to bringing new payment methods to existing merchants without having to educate them on how it works exactly. I can see this working but I'm not sure if this is viable right now. The exchange rates are too volatile and even if you used gox api to position a merchant 50/50 coin / USD it could prove difficult to sell the coins. It only takes a small group of people trying to sell all their coins at x fixed price to drive the entire market down and leave you unable to crash out.

This is a good concept and I'd love to see it turn into a reality, bumping this up.

+1