"letting users easily control HomeKit-connected devices from their living rooms through the Apple TV dashboard"
Yep, super easy... "Hey, Honey, can you turn the lights off?" "Yeah, let me just head downstairs, turn the TV on, turn the Apple TV on, and turn the surround sound receiver on. Then after it loads, I'll fumble through the dashboard because the Apple TV remote buttons are too small... Wait. What did you want me to turn off again?"
Seriously. Even if you were already watching cable, you'd have to switch HDMI inputs to get to the Apple TV, then go through this process. Or even if you're watching a movie on Apple TV, you still have to leave that movie to access the HomeKit.
I would think using your phone or an iPad mini that controls the house is probably a bit easier.