Interesting, but can someone tell us what this implies wrt. authorities? If someone gets your iPhone and forces you to press your finger on the TouchID, he gets all your passwords no? While with a general master password you could just pretend to have forgotten it?
Besides that, it is not needed to force you to press your finger; the delinquent needs only to have access to the device for to fool the sensor with a brute force, 2 hours in the worse of the cases with the simplest techniques. Although its easier to take your finger prints from a glass or something you used for to avoid the wait, or directly cut your finger if its a psychopathic criminal.
And in all the cases, once your fingerprint gets public it gets compromised until the end of the times, of course, you can not "change the passw".
This without talking about software infection with a remote attack.