Given the breadth and range of female voices available, this is way too close to be just a coincidence.

There are approximately 4 billion women in the world. Given that I know a few people who sound very similar to me, I would say that there are (subjectively) perhaps 1,000 to 10,000 different types of women's voices in the world.

This would mean that a celebrity could possess a voice similar to 0.5 million to 5 million other women, and potentially claim royalties if their voice is used.

This types of estimate is sadly deeply flawed. Voices are affected not just by ethnicity but also language and culture. I know because I can feel slight noticeable differences in tones between communities just 30-50 miles apart, within same social classes and everything. Bilinguals also sound noticeably different to monolinguals even in their primary language.

I think people thinks others sound same not because they're similar from beginning, but because voices must homogenize under peer pressures. There's a proverb "nails that sticks out gets hammered". Most people probably has hammered flat voices intended to not stand out.

fine. So the entire casting process for this role picked a 1 in 10,000 match for Her. That's not coincidence

You first said that Sky is "clearly an impersonation" of Johansson. Now you say that it's not a coincidence they chose Sky's voice actress. These are two different claims. It may not be a coincidence in the sense that they may have chosen Sky's actress because she sounds similar to Johansson. But that alone doesn't constitute an impersonation. Impersonation means deliberately assuming the identity of another person with the intent to deceive. So you'd have to demonstrate more than a degree of similarity to make that case.

Isn't it TTS + style transfer? Or is it e2e from text to waveform?