In the first developer beta of iOS 16, it was already indicated that Apple would introduce changes to Home that would affect the iPad as the home control center. Now the company confirms that the iPad with iPadOS 16 can no longer be used as a control center for HomeKit.
No manual activation in 2nd beta more
While the iPad could be explicitly reactivated as a control center in the settings in the first beta of iPadOS 16, this function is no longer available in the second developer beta. If the Home app is started with iOS 16, users are now informed that the iPad can no longer act as a control center. So far, an iPad that is used permanently at home, a HomePod, a HomePod mini or an Apple TV (4th generation or newer) can be used as the control center, with Apple automatically selecting a device if there are several in the network. The rest then remain in standby as a replacement. A control center is necessary to use automations and remotely control connected devices in the home.
A home hub is required to take advantage of features like receiving accessory notifications and allowing other people to control your home. You will not be able to view shared homes until those homes are also upgraded to the latest HomeKit. iPad will no longer be supported as a home hub.
Note from Apple in iOS 16
Apple has revised the home architecture
Apple doesn't give reasons for the end of the iPad as a control center, but on the iPadOS 16 website Apple states that it has updated the underlying architecture of Home to offer faster and reliable performance that makes smart home devices more efficient controllable from multiple devices, especially in homes with many smart home devices. These changes, along with upcoming Matter support, could be a reason behind the change. Because when supporting the future smart home standard Matter for unrestricted interoperability and compatibility across manufacturer boundaries, Apple explicitly mentions the need for an Apple TV or HomePod as the control center (Notes 11 and 12 on the iPadOS 16 website).