I have to believe that HomeKit has fallen so far to the wayside due to their work on Matter. And we can expect something big in the near future. Right? Please?
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.
I'm not sure how Apple would approach this though. Would it be part of your iCloud data and require a minimum plan (similar to how HKSV operates). I don't ever see them allowing the option to control /where/ that data is stored exactly.