Debit card interchange for big bank debt cards is 0.05%. Sites/stores/apps don't offer debit cards discounts except gas stations. Big merchants offer their own payments/credit cards for up to 5% cash back, they aren't going to switch.

FedNow will get adoption as a replacement for ACH / Check writing. Paying bills and getting paid. Instant deposits of paychecks will a big benefit to a lot people living paycheck to paycheck. It will displace a bunch of Zelle market share.