These are the rules far as I know:
Main hub for application purposes is supposed to be the Apple TV.
Anything that's strictly a wifi gateway is not gonna be supported. So Hue, DropCam, Nest, etc won't work.
Anything Homekit certified is not supposed to include other protocols like Z wave. So Insteon isn't supposed to be putting out a hub that talks both Z wave and Homekit. I'm guessing powerline carrier doesn't count as a protocol which is why Insteon devices still work
You can bridge Z-wave/Zigbee by adding a special bridge but you can only talk to sensors. You're not gonna be able to use the bridge to unlock your Z-wave deadbolt
Anything that can be controlled needs to be controlled through HomeKit only. So if you have Hue lights, it isn't enough for the Hue hub to be upgraded. Every $60 bulb in your house has to have that proprietary chip
Yes, I read most of that before as well. Im not sure how or practical that may prove for many home automation tasks.
The key part of HA is the word automation. Its a process that happens automatically, on its own, all the time. You set the living room lights to come on at sunrise every day and to go off by 11 PM. So something has to be both alive/awake and accessible generally to perform this task. In the past this was usually done in one of a few ways:
1. Local PC runs HA software and performs tasks on a schedule.
2. Local HA hub has schedule imbedded and performs tasks
3. Some other approach
Another key part of most HA areas are triggers based on home activity. Things like motion sensors, window/door sensors, leak detectors, etc. There is no schedule for these devices, only the event and the desired process that follows lights coming on, doors being locked, alarms being triggered, calls being make, notifications being sent, etc. Its a long list.
In the past most of this occurs within the actual home using gear located there. Some exceptions for things alike alarms and alarm companies exist, but still rely on the gear inside/part of the home for detection. It occurs where the residents are there or now, regardless of the state of their phones or connectivity. That might prove to be a difficult task for an iOS device that moves around, eats battery, and goes in and out of connectivity. Light sensors have to work whether or not an iOS device is traveling through a tunnel for a few minutes.
Apple TV is an interesting part of this upcoming kit. The new one is said to be a key player in the HA area acting as a hub of sorts for control of devices. That would be a substantial change in the way that ATV works today, as it goes to sleep usually after a short while when there is no user activity. It would instead become an always on device, basically with many if not most PC alive features for always running tasks. That alone is required for Siri.
I see the ATV being a good source for manual controls based on things like voice commands, but maybe less so for the background automated tasks. Maybe this will work fine, but well have to wait to see what is introduced at WWDC in a few weeks.
The other interesting part of ATV is the possible option for a took kit and developer created apps. If these apps have access to the same hub features, then developers could make the app do just about anything based on what external devices could be acccessed/tracked.
Another key aspect of all of this is 2 or more iOS devices. Consider Nest as a simple example and the setting for Home/Away. Using GPS this becomes fairly easy for one person and one iOS device. The person leaves, GPS detects, and away mode is set. The person returns, GPS detects, and home mode kicks in. That works fine. Then there are 2 people and 2 iOS devices. This becomes harder as you have to somehow know whether both are gone for away mode. It requires more, and gets even more involved when there are 3+ people and potentially many iOS devices. Its solvable, but takes a lot more than the one user case.
For HA tasks this is much more involved. While Apple uses the cloud for a lot of features and capabilities, it may be less suited for HA tasks. There are some normal delays with using cloud data from one device posting a change to other devices being notified of the change. If you enter a dark home area, you really dont want to have to wait for 30 seconds for this process to complete and the lights come on. You expect 2-3 seconds max.
Time will tell how all this works out for HomeKit. However for many of us who have been involved in HA software for decades, there tends to be a lot more to it than most realize.