Google has to incorporate the functionality of wifi calling into the software for the Nexus 6p just like they did for the Pixel phones. Even then I'm not sure how well they did on the Pixels.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.
The 6P is WiFi calling enabled, and it works great on many carrier plans. Verizon just won't add the phone to the list of "accepted" phones.
This one is all on Verizon.
Google didn't give Verizon an exclusive and priced the 5P and 6P too low for Verizons desires. So Verizon grudgingly allows the phones on their network but they won't enable advanced features like WiFi Calling. They did enable HD Voice, but only because they are trying to move all traffic to VoLTE so they can shutdown/refarm their CDMA assets.