Earlier quoted context omitted.
Since the courts decided you have to use your fingerprint to unlock your phone (because they decided that's not giving up your password and they can't compel you to give up your password), what if you use your fingerprint to wipe your phone? But you don't tell anyone ahead of time when they force you to use it. I'm sure you'd be arrested at the least. I can't be the only person who has thought of this.
A password is considered (by courts) to be testimony. Face, gesture or fingerprints are considered things like keys which you can be forced/compelled to turn over when commanded by law enforcement. Therefore, only passwords, which will require a court order to unlock, are secure enough for now.
For now. It doesn't seem like an especially natural fit. Regardless of the merits of being able to compelled to turn over your password, relying on labored interpretation of laws is not a good idea: 14th amendment was always a very shaky basis for abortion rights, as the 2nd is a very shaky one for personal gun rights.