Bluetooth devices on iOS that display notifications already are getting more information than normal by simply even reading all notifications. Normal apps on iOS can’t do that, they have no reason to. This api was added because smart watches kinda need that functionality to be useful. I think it’s still locked behind a “this device will see all your stuff” permissions box.
I do think they should add in more iMessage/sms/replying capabilities to smart watches though. I think they are extremely hesitant to make it even easier to automate iMessages. iMessage spam is definitely increasing, but it’s NOT as prevalent as normal sms spam for instance. The barriers are much higher, and Apple can basically blacklist devices/appleIDs that send out too much spam, partly because they’ve kept iMessage so locked down.
Apple doesn't need outside ecosystem builders here; what is the business reason for them to add process expense, risk, and possibly incorporate timelines from other vendors into their supply chain?
As the many comments in this thread indicate, lots of people seem to feel Apple "owes it" to the world to open up. Happily, there is a (more) open ecosystem available with Android for people who value that. I don't think the tradeoffs Apple makes are perfect for me as a consumer, but I prefer them to the Android tradeoffs, and I can always switch when I like.