A recently discovered patent application hints at Apple Watch possibly getting in-display Touch ID for an additional level of security. The patent refers to "a touch sensing device, force-sensing device, temperature-sensing device, and/or fingerprint sensor" that can be placed behind the screen. It doesn't seem like a far off idea given that the Apple Watch already supports Apple Pay.
The patent describes having the wireless antennas on the watch moved to the strap so there will be room for more components under the screen. There is a caveat there, though. Moving components like Wi-Fi, cellular, and Bluetooth to the strap might affect its uses, given the wear and tear as well as the customizability Apple offers. But this is just a patent, so perhaps it might not see the light of day.
Source: TechRadar