Patent application hints that the Moto Z (2017) will sport an iris scanner
The iris scanner can basically do the same things that the fingerprint scanner can do except that it reads the unique characteristics of the user's iris to unlock the phone, verify identification and open apps. We should point out that the sketches in the patent show that the Moto Z (2017) will continue to sport a dedicated front-facing fingerprint button (as opposed to a home button with the fingerprint scanner embedded inside).
The next version of the Moto Z is also expected to keep the compatibility with the modular Moto Mods accessories. Considering that the current Moto Z line was unveiled last June, we still have a few months ahead of us before the Moto Z (2017) series sees the light of day.