Have you heard of this?
Social graph analysis has advantages over biometrics. The main advantage is that it doesn’t require the oversight of an organization to either administer or verify the biometric checks. The structure you’d need with biometrics would be very similar to the structure you’d need for KYC.
“Manual KYC checks are cumbersome and subject to manipulation. They would present a weakness in the system, since we end up needing to trust a third party to verify an individual’s uniqueness”
This applies to biometric checks, also.
“We don’t really care who they are, in fact it’s probably best to preserve individual anonymity but we want to make sure that they are unique.”
This should be the goal. Social graph analysis could be done in a way that preserves anonymity.