Card emulation is a thing now: https://developer.apple.com/documentation/corenfc/cardsessio... (edit: only in the EU)
And iOS as well as iPadOS now also support USB smart card readers. iPads can actually use them to access NFC FIDO tokens. (Why iPads don't have native NFC is completely beyond me, there are so many obvious use cases for it)
Oh, that's very cool!
Apple seems to silently be implementing more and more features to make iOS/macOS a full-fledged smart card OS; I've also noticed that FIDO over CCID is now available natively on macOS, and by extension in Firefox and Safari via WebAuthN (which finally lets me use my smartcard form factor FIDO authenticator).
If you can send/receive APDUs you're good to go.
Do you know if Apple requires any special permissions/entitlements to create VAT passes, or does a normal pass certificate suffice?
At least Suica train cards(based on FeliCa/NFC-F) on iOS can be read from third party Android apps, and Apple do advertise iPhone feature to store corporate IDs, so the idea of using iPhone for gate tap-in card should be completely fine.
It's not accessible to "regular" app developers in the way it is for Android.
ISO 14443 reader access has been available globally, so if you're fine with having to open an app before an interaction with a reader, you could have the reader perform card emulation, and the phone "read/write" it like a tag, i.e. send APDUs which the device behind it then interprets.