Playing devil’s advocate a little bit here - are you saying a person’s voice is or should be copyrightable? Because it wouldn’t be his voice, it’s an imitation of his voice, it’s an impression.
I’m just not sure this is an area that copyright law needs to be extended in to. I can see a requirement to disclose that it’s AI generated being a good idea, but the idea that the likeness of somebody’s voice is proprietary I think opens up a much worse can of worms.