All that's needed is for a new interloper to charge very low interest to consumers and very low fees to vendors. Visa and Mastercard would evaporate away like the morning dew.
Just like Kodak didn't see disaster coming, Visa and Mastercard also think they are invulnerable.
suprisingly india with its "UPI infrastructure" has mastercard/visa/paypal in a bind and very anxious because you suddenly do not require "a massive infrastructure to maintain the financial network and requires 2% cut".
at the scale of india's daily transactions, 2% is a lot.