Australia implemented Osko from scratch in 4 years and it took maybe 2 more before every main bank was using it. There's no need to wait for everyone.
They did https://en.wikipedia.org/wiki/Zelle
> The initial release of the FedNow Service provides baseline functionality supporting market needs for a range of use cases, including those growing in demand such as account-to-account (A2A) transfers and bill pay.
https://www.frbservices.org/financial-services/fednow/about....
I've never seen Zelle suggested for bill pay. I've tried to use Zelle for account-to-account transfers, but it was obvious this wasn't the intention; I think I had one bank account tied to my email and another to a bank account tried to my phone number so I could send money to myself (the intention seems to be a person only sends/receives from one bank account) and the limits are very, very low. When I was trying this, the cap seemed to be secret and vary institution to institution.
[1] https://www.zellepay.com/faq/there-limit-how-much-money-i-ca...
Separate from this, wire transfers are near-instant during business hours. Most banks surcharge these for standard customers, but all the big banks have wire fee waivers on certain account tiers.
There's also the "accidental" transfer method of over-refunding a debit card, which used to be a sketchy fintech trick but is now straight up supported by Visa.
Sometimes they offer bill pay services which don't guarantee prompt delivery (in fact, often imply that they might fall back to sending a physical check through literal postal mail), but in practice frequently enough do go through instantly by whatever means the bank happened to find convenient.