According to Google, the Nexus 6P firmware is why the Nexus 6P is not able to support fingerprint gestures despite having the same hardware that is being used on the Pixel. Oh and we already have a work around thanks to the developers (Bring the notification swipe gesture from Pixel to 6P (No root required))
Though this is the official answer from Google I am calling bull because they could have changed that in an update. Also given the fact we have a number of people who are experiencing battery issues such as their phones locking up or weird drain issues right when Google is trying to sell their $900 Google Pixel without $900 features seems kind of fishy to me.
Thoughts below.
Source: Here's why Nexus 6P and 5X aren't getting fingerprint gestures