HomeKit's biggest challenge is that so much of the home automation market balks at Apple's requirement to be able to operate without a cloud service. Can't do surveillance capitalism or extort monthly fees or end-of-life product arbitrarily if you've got HomeKit branding, so of course that's first overboard.

The second problem is that Apple themselves are missing a number of functions that are baffling, such as not having history for metrics. I can't understand how it's impossible to have e.g. a history of temperatures in HomeKit.