Your idea would best be implemented into a crypto-coin wallet hosted online, which allowed for merchant API access. It's there that this would be the easiest to use, and code.
OK, that piece of technology makes sense. But question is, would a merchant ever prefer this form of subscription billing over the customer entering a credit card number? Sure the 2-3% can be saved, and sure there is no chance of fraud, but in an ongoing subscription billing service, most businesses don't need to worry about fraud.
So what is the value to the merchant?