500 watts continuous isn't realistic, unless you foresee a 24/7 digital shadow society where AIs interact continuously without user input.

Really the METR report on autonomous agent behaviors is a required read.

I think the AI's would only do a tiny percent of their talking to their human. Voice itself is only a limited method that we interact with the world. Imagine the LLM seeing what you see, monitoring your health, monitoring your interactions with the world around you and then optimizing around that. For these things it will be talking to its own agents/subagents and the AI agents that operate the services of the world in this imaginary world.

Maybe you also think of it as a self contained business that provides services to you. Even when you're not busy consuming services from that business, that business typically keeps running and doing things for when you need it next.