SSH authentication using biometrics

This sounds like a really interesting experiment. All the parts are available, although I don't know of anyone who has stitched them together. First of all, I would use the x.509 biometric consortium's approach.

Effectively what you'll be doing is creating a private key which is encrypted using a key generated from your fingerprint; then using that key, once decrypted, as a standard x.509 private key. This means that you won't need to modify OpenSSH so much as provide a custom method of providing the private key to it.

Unfortunately, out of the box, OpenSSH doesn't support x.509 authentication. However Roumen Petrov has fixed that here.

I've done both things independently and they work a charm - I've not tried glueing them together though. I suspect, as you allude, it may not be worth the effort.