I've been playing a bit with the banks I mentioned above. So far I've tried Revolut and Openbank and I'm happy to report that Openbank works on GoS without Google Play Services, including NFC payments. The app gives 'this app requires Google Play Services' popups on some screens, but everything works.
It does behave a little odd, where it initially rejects the transaction until I unlock the phone, even though in system settings I've disabled that the device needs to be unlocked for NFC to work. But maybe this is just a requirement of the Openbank app, I'm not sure.