In theory, even though this may sound very far fetched and Star Trek... You can walk up to a shop clerk, tell him what you want to buy.. They then scan your face and it links you to your bitcoin address, and to
confirm your purchase, you have to press your finger on a biometric fingerprint scanner... or the same scanner just zoom into your iris and confirm the payment.
It would be difficult to bypass a physical one-on-one transaction like this.... Face = username / Iris = password / finger print = 2FA.
The face recognition software takes several features into consideration when it verify your identity... if it finds a 90% match, it fills in the "username" ...This can work.
What happens when your facial profile and your fingerprints become compromised, more transplants? Gene therapy for new fingerprint patterning? Maybe we could all walk around the whole time wearing masks and gloves?