I think it's the classic argument that a premium cardholder typically spends more money than the average customer and therefore they're more profitable to the merchant. Which is probably true to some extent, so the merchant willingly pays more. But with some swipe fees approaching 4% for certain cards it starts to get ridiculous from the merchant's perspective.

I have 11 credit cards accumulated over the years and 9 of them have some sort of reward or rebate. Only 2 are plain vanilla cards. But I won't be canceling those 2 vanilla cards since I may have to use them at some point to avoid an upcharge at certain merchants. (The vanilla cards are more likely to have 0% promotional APRs, which is free money if interest on savings is better than average).

Most upscale merchants will just ignore this settlement (if implemented) and continue pricing their services accordingly.