You’ll likely run into ‘likeness’ issues if you use actual celebrities’ voices, especially considering that it would cut into their own book sales. I imagine many authors have self-narrated their own audiobooks and don’t want others to undercut it.
I think this might be better suited for public domain books from the past. If I could have The Count of Monte Cristo read by a Frenchman (in English), or Sherlock Holmes read by a British man with a Victorian accent, that would be cool.
Also another idea: audio versions of movie scripts. Select a character type for each role in the story, then automatically generate an audio version of the entire thing.