I would expect Siri to be able to do anything on the iPhone that I can - change settings, report stats, kill/launch apps, etc.
It would be nice if it could control 3rd party apps too, like GMail, but being able to control the stuff that Apple themselves have built doesn't seem a lot to ask.
Apple is somewhat privacy focused, allegedly. I would imagine that letting an unpredictable LLM read whatever system data it wants is not something they want to partake in.
Maybe there are different concerns now that Apple are apparently going to be using Google LLMs for Siri, although I'd have thought that any access to system settings or other iOS functionality would be via tool calls with user opt-in.
However, the original Siri, obtained from SRI ("Siri" = SRI) was pre-LLMs, and there should have been no more concern over accessing system settings or controlling apps than things like reading/sending messages. For some reason Apply completely dropped the ball with Siri; initially it was expected that they would expand it into revenue generating areas like restaurant reservations etc, but then nothing. I'm not sure what documentation exists, but even today it's not clear what Siri is actually capable of.
It would be nice if it could control 3rd party apps too, like GMail, but being able to control the stuff that Apple themselves have built doesn't seem a lot to ask.