Apple looks to be positioning Apple TV as more of home automation hub than previously thought because the company plans to use the streaming media box as a bridge between HomeKit and non-homeKit devices. That support means more devices without official HomeKit support can be part of your smarthome setup, but with some big limitations.
Apple TV will bring non-HomeKit gear to your smart home network
HomeKit is Apple's platform for standardizing communication between smart home devices such as thermostats, lights, and door locks. Any device with Apple's MFi certification can be part of a HomeKit network, and that network can be controlled locally or remotely through your iPhone and Siri voice commands.
Issuing Siri commands to your smart home remotely will require a third-generation Apple TV to bridge between your local network and the Internet, and it'll serve as the bridge for non-HomeKit gear, too. That means devices designed for the Z-Wave and Zigbee smart home protocols will work on your HomeKit network, although Apple has some pretty serious restrictions in place.
Any non-HomeKit device that offers some sort of home automation function, like a smart thermostat, remote lock, or even smart lights, won't be supported. In other words, this isn't a workaround to add a Nest thermostat to your future HomeKit setup. Instead, Apple is limiting support to data collection devices and gear that enhances your home experience instead of controlling it, like home theater speakers.
The reasoning behind the strict limitation seems to be security related. Without MFi certification, Apple can't ensure your smarthome network is safe from outside attacks. Keeping someone from hacking your HomeKit network to unlock your front door is no doubt a serious concern for Apple.
HomeKit smart home accessories are expected to start shipping soon, although Apple hasn't announced an official launch date. Developers like Belkin and Philips are saying they're committed to the platform and have hinted that they're very close to launching their products.
[Thanks to 9to5Mac for the heads up]