I think there are probably some ways to cross over a bit, but really, LLMs aren't necessarily aimed at the kind of things we want a virtual assistant to do today. Siri falls down mostly on its ability to correctly do things quickly and reliably. Generating 5000 words of convincingly human sounding explanations isn't what I want from a thing I quickly trigger on my phone. What I want is very short or no reply accompanying the action I wanted to take. Call this person. Start navigation to an address. Turn on the lights. Play the version of a song I like from this specific live album. Some of those things are things Siri really sucks at today, and none of them are likely to get a lot better with an LLM in place. Maybe playing music benefits from a more robust understanding of the language of my query, but the rest of it are things where the suckage is more that Siri takes 8 seconds for the server to respond or just inexplicably decides that today it doesn't know how to turn on a light.

At this point it feels like a great LLM would let Siri fail to respond to a much more varied set of ways for me to ask my question in English, but that's not really the target we're shooting for here.