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.