You can already somewhat do that with iOS and Shortcuts if you have the chatgpt app. But as OP says, it’s only to talk to. Can’t use it to set a timer or reminder. It’s neat but a lot of my voice assistant stuff is “call X person” or “reply to X”. If I want to talk to chatgpt, I usually open the app and turn on voice for a session.
If ChatGPT can weasel itself into a true assistant with the ability to perform certain actions, then it might be a game changer for the voice assistant space. It’s so much better at understanding context than current assistants on your local device.