Right, this is definitely the way it already is for merchants.

The hard part is knowing what you'll pay. In most cases, you can't tell what percentage you paid on any one card until after the transaction has cleared, and even then, it's pretty hard to dig through reports and get the real number.

This is why it is often said that the poor subsidize the rich in regards to cc rewards. The rich use premium cards which cost more and accrue mileage or other perks or money equivalents (or money). The poor use standard cards or debit cards which costs merchants less. But merchants average the costs.