I will try to add some context here that will hopefully help people to understand the limitations of CoreNFC.
Functions absolutely NOT possible, as the CoreNFC API is read-only:
*Yubico Authenticator (no TOTP)
*U2F
*OpenPGP
*PIV
*Challenge-Response
The only that that could possibly work using CoreNFC is the slot-based button press credentials - Yubico OTP / Static Password / OATH-HOTP
The CoreNFC API is available from an app that explicitly calls it. That would mean that if Yubico came up with a YubiClip for iOS (example), the app would have to be launched by the user, then the YubiKey NEO could be tapped, and the OTP copied to clipboard. This adds a lot of extra steps over the Android version, where you can just tap and then immediately paste.
Where the CoreNFC API becomes more useful is for a third party app which supports Yubico OTP (example: LastPass), where the app itself calls the API when the user authenticates. This enables a more seamless user experience with NFC-based 2FA.
Yubico developers did just publish source code for a proof of concept of intercepting a slot-based credential:
https://github.com/Yubico/ios-yubico-otp-nfc-demo.