would like to know which variable type comes closest to representing biometric binary data? Assuming computing storage and power grows exponentially and network latency can be further reduced, would it be possible to store one,s private key as biometric thereby enabling a web of decentralized identities?
Your question cannot have a unique definite answer.
In biometric analysis you need to fix some minimum and maximum treshold for data complexity in order to fix the unicity of your identifications.
Think to the complexity of a fingerprint analisys versus some facial analisys, versus some like rapid-DNA Analisys and so on.
Different recognition targets (in terms of identification precision) give you very different complexity amount in data representation and suggest you to use different techniques for measuring that information.
In general the answer is "yes, surely it is possible to have those data on a blockchain", but "how much precise" and "when (2018 or 2028...)" is very relevant in order to choose the proper binary representation.