Look at AMEX, which has been rebuked by many merchants due to higher fees. The biggest risk for Visa & MC in doing this is that AMEX might begin to seem more swallowable for merchants.
Amex actually lowered their fees to be more in line with Visa/MC through its Optblue program back in 2015. The fact that many businesses don't know that is just a testament to the complexity and confusion in the industry.
We don't know which rates Visa/MC are actually raising yet, but probably not. It has a lot to do with how/what processors charge.
Along with lowering costs, Optblue let processors add a markup to Amex transactions. (Previously they couldn't. That meant no incentive for processors to suggest or push Amex acceptance, as they didn't make money on Amex transactions.)
Now they can, and those markups tend to be higher than for Visa/MC. In egregious cases, the processor simply continues charging the business the old Amex rate (~3.5%) and pockets the entire difference between 3.5% and the new lower rates.
