In a new article released by Apple today, "Developers Preview New Ways to Make Payments, Send Messages and More Using Siri", they released a few previews on how a few payment providers have created a Siri experience for their service/app.
Developers are previewing new Siri integrations for payments, messaging apps and more, creating new experiences using “Hey Siri” to simplify everyday tasks using just your voice. Siri can already help you send an iMessage to a friend, but with the introduction of SiriKit for developers, messaging apps can now tap into the power of Siri. You can use your voice to do things you couldn’t do before, like ask Siri to send a secure payment without ever opening an app.
I'm really happy to see Monzo (formerly Mondo) on the list, and they've proven to be a really forward thinking (now official bank) service!
There are a few more previews in the article as well, which aren't for payments, but show some future third-party integration with Siri.
With all of these integrations coming to Siri, it may finally become useful.