This is not a new API AFAIK. The Payment API[0] has been around for a while. MDN's got the full skinny [1]. [0]: https://webkit.org/blog/8182/introducing-the-payment-request... [1]: https://developer.mozilla.org/en-US/docs/Web/API/Payment_Req...
Is this intended for actual non-Safari browsers like actual Chrome or Firefox on iOS or just what there is now where Chrome and Firefox on top of the same WebKit engine as Safari?
But this would mean you could use ApplePay from the current FireFox app.