Very unusual case use, but my mother can't use TouchID on any device. She's been to Apple Stores many times, and seen the Apple Community forums from others with her issue - she does have a fingerprint, but it is quite worn. She can train a TouchID device and use it 4-5 times within 5-8 minutes. After that, it fails to recognize her fingerprint and she has to set it up again. Her fingerprints apparently don't have enough definition to make a consistent map. There's a whole community of people like her [plus people w/o fingerprints!] who can't use any TouchID or TouchID-like system. So for those edge cases, FaceID would be wonderful [she uses an older mini but types her passcode to unlock it - would love a FaceID 7th gen mini with an M1 or M2 inside!]