If you haven't tried OpenAI's advanced voice mode, it's a mind blowing version of exactly what things like Siri really ought to become with a little more development. If that's what you mean by LLM Siri, I totally agree.

Being able to chat casually with low latency, correct yourself, switch languages mid-sentence, incorporate context throughout a back-and-forth conversation etc. turns talking to these kinds of systems from a painful chore into something that can actually add value.