Speaking as someone who tried (and failed) to build a competitor, merchants don’t actually care about the fees. We built a mobile payment system using bank transfer rails (ACH debits and FedNow credits) for ecom platforms. QR payments, just like AliPay, but for the US. We studied past failures at this same idea, and targeted specifically high ticket items (jewelry, luxury), because the fees are a bigger problem, and…
Crypto has value the way Gold or pawnable items do, and until that barrier has been crossed the people will never embrace crypto as an alternative to cash and credit.
Realistically the only way for that to happen would be if the US replaced their currency with a government backed crypto, but that is unlikely to happen without a coup.
Visa and MC could still offer lines of credit in such a system but they would not be the primary purveyors of capital motility and therefore their entire business model would collapse or require extensive restructuring.