Just thought since the phones can be unlocked with faceid this technology would be safe enough for wallets. Now I see this idea has many edge cases. Nevertheless, I still think they will solve the mentioned issues someday...in the future...with enough funding...
it's just a matter of beating you into telling which body part.
best case: armed robbers wrench attack you, you give up the biometric auth, they sweep the funds there.
worst case: armed robbers wrench attack you, you give up the biometric auth, they remove the body part in question.
New startup idea: mobile magnetic shields which would protect from such "armed robbers"