AppleTV as the home hub (this will be the big news of WWDC, imho). Then a proprietary system with a sub-hub for their devices. Makes sense this branched architecture. The second (third, fourth..) hub acts as the interface between HomeKit and the things they make. So, they need to certify just the hub, not a lot of other stuff. These thingies can be 'light' in this scheme, with all the protocol complexity managed by that sub-hub.