Unfortunately, we heard back from them that there is currently no API available for integration with home automation systems. We'll continue to try to work with them, but without an API it will make integration much more difficult.
Very much in the Apple Way, they want to provide a whole experience, rather than ship a component in a system they don't control. I don't mind reverse-engineering their IP interface. I'm just afraid that a lot of the raw sensor data never makes it off the device, making it necessary to hack the Nest itself.
We'll just have to see...