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.
The ai is trained on recordings of his voice which they have not secured the rights to though. You can't simply use any data you find on the street and use it professionally in any field.
An impression is a very different context. You're vastly overestimating the independence of an AI model to equate it to human performance or impersonators.
You can’t simply use any data you find on the street and use it professionally in any field.
I kind of think you should be able to though, copyright laws are already much too strong and outdated with current technology, instead of strengthening them further I think we need to go back to first principles and consider why we need to have permission to record and relay what we see and hear.
But isn't Attenborough's narration dependent on much more than what you can get from a few seconds? I imagine that you would also want to get the same narration style, e.g. how his voice/intonation relates to what's happening etc.