Aside from specific banks having their own implementations, this is hard to do. Not necessarily from a technical perspective, but more likely not something that someone wants to invest in.
That said, there was very recently this:
https://reddit.com/r/ProtonMail/comments/1eayqs4/proton_wallet_early_access/leoxa7i/
Proton apparently made a Bitcoin wallet app (very weird in my opinion, but hey). When asked whether they'd want to compete with Apple or Google Pay, a representative said:
This may come later, subject to certain licenses being obtained, and community feedback. As hinted in the blog post, we hope this opens the door for further work in this direction.
Perhaps if they do eventually decide to go towards that direction, they don't artificially restrict it the same way Google Pay is, and is therefore an option that can be used on GrapheneOS. It would likely result in a lot of subscriptions just from GrapheneOS users alone.
All of this of course hinges on many factors, and if I'm perfectly honest, I'm not that hopeful.