I haven't used any of the other modes on my Yubikey 4 than the OpenPGP Smartcard. I would hope that other modes also support PINs/passwords, so the fingerprint

I haven't used any of the other modes on my Yubikey 4 than the OpenPGP Smartcard. I would hope that other modes also support PINs/passwords, so the fingerprint is just an additional factor. If that's the case, it's not necessarily about replacing passwords with fingerprints.