I've thought about one, but an IT security friend of mine is concerned about a few things, such as the data that Google gathers about you. I mean you personally.
Here's an example: you use a Google service, it could know that
you are home based on your heat setting+IP address+location services+logged into a G account.
It's not the NSA that I'm concerned about. There seems to be at least some checks & balances. Corporations, on the other hand.....
Also, it's not like Nest, or anybody else, hardens these devices to prevent security intrusions. That's what hackers look for - the weakest link.
Hope that's not too much of a downer.
Sent from the driver's seat of my car while in motion.