Geofencing on the Caseta app does not have the ability to control Nest devices. You can only control the Nest thermostat from the main screen of the Caseta app. Geofencing can only trigger manual scenes that are programmed to the app.
Also, geofencing doesn't have the logic to detect that someone is still within the radius when someone else enters or leaves. If you have geofencing on, and someone crosses the set radius, the system will trigger whatever scene is programmed to be triggered, no matter if there is a second person in the radius or not.
Here is a link to our list of approved LEDs that our dimmers can dim:
http://www.lutron.com/technicaldocum..._Bulb_list.pdf
See pages 46-59 for all three of the Caseta dimmers.
We are looking to expand the Caseta line of products over time. I will forward your suggestion for a fan control, and Google Weave, over to our engineering department. Thank you for the suggestion.