It's one thing to copyright a performance or own a likeness. Owning the sound of a voice is scary territory we do not want to get into, or the estate of every singer will be suing the estate of every other singer who will be suing the remaining actual living singers.
Thinking about replying to this comment? Don't make your writing style sound too much like mine, I have lawyers standing by. And all you trendy kids that type without caps and punctuation can expect a visit from the estate of e.e. comings.
I think though that Sky's performance is similar to ScarJo's performance in Her. They're both playing AI voices.