Settlement between banks in the United States is astoundingly complicated, for (fascinating, terrifying) historical reasons. FedNow is a huge step towards fixing holes that private companies have been papering over for over two decades. Blatant self promotion: for anybody interested in learning more about the Automated Clearing House system (which FedNow will eventually supplement) and interbank settlement in general…
You say “FedNow will eventually supplement”, and I read through your post, not too thoroughly, but I liked it and saved it to my Pinboard archive. Why couldn’t FedNow eventually replace the system you described though?
It's possible that some of the more obscure abilities of ACH, like death notification entries[1], won't be needed in FedNow or will be replaced separately. But that's idle speculation on my part.
[1]: https://www.moderntreasury.com/journal/what-happens-when-you...