Siri could benefit from LLMs, and given Apple's customer base, an LLM-powered customer support could help them provide answers to questions quickly and only forward the tricky ones to human customer supports, saving cost and time for Apple.
When it comes to autocorrect, the situation with iOS is a joke compared to Android and even Windows. A better AI-powered autocorrect could put Apple on par with Google and Microsoft.
Some might say Apple is secretly doing all of this, but given the nature of such models, I find it difficult to believe that Apple wouldn't open-source [part of] their model.
There's just so much going on in AI and the hype around it is mostly exploited by Apple's rivals, while Apple has been mostly silent and irrelevant.
Apple is a human-centric company and no one likes talking to robots so if they can afford a customer agent for their calls then why would they add an AI as a go between?