[ AGC (PDF) ] Asahi Glass launched a smartphone cover glass with a recession on its underside to accommodate a fingerprint sensor. Now the top of your smartphone can be completely smooth top to bottom and still have a fingerprint reader.
The only challenge might be to locate the fingerprint reader if your eyes are on the road. I locate the fingerprint reader on my iPhone by touch, not sight. Perhaps if there was a thin circular laser etching where the fingerprint reader is on the cover glass?
With Apple’s Force Touch and AGC’s multi-thick smartphone cover glass design I can see a future iPhone with a completely smooth front. Except for the speaker cutout toward the top for your ears when you use your iPhone as a phone. Maybe someone will find a way to develop a smartphone cover glass that can pass sound waves.