[throwaway6977]

What is preventing any of those mentioned card vendors from integrating with FedNow either directly or via some abstractive layer through another entity? I don't understand why the answer would be 'no for these reasons'.

[matthewdgreen]

The retail payment companies I've seen all use the same structure: they provide a retail interface and then handle monetary transfers within their own proprietary network (effectively a centralized database). To interface with the financial system, they provide a mechanism to occasionally wire funds to/from a traditional bank account. If FedNow has any role in these systems, it's just to speed up the occasional funds-wiring process by a few hours. I have yet to see anyone actually directly using FedNow in any meaningful sense for retail payments.