Google has introduced support for Nest integration through their Smart Device Management (SDM) API. It costs $5 to register, but is available at the following link:
The documentation and discovery document for the API can be viewed here:
https://developers.google.com/nest/device-access/reference/rest
https://smartdevicemanagement.googleapis.com/$discovery/rest?version=v1
Finally, there is a thread discussing this in Third Party Integrations:
https://community.home-assistant.io/t/google-nest-offical-device-access-console-finally-released/
It would be great to finally get true Nest support, including using people/motion detection and doorbell presses as triggers!