That's a good point. I'm already in the process of using voice synthesis to narrate one of my books. It is still a huge time outlay to get to the quality bar I want, but much cheaper than paying for a narrator.
One thing working in favor of human narrators is the fans. Audiobook listeners can get very attached to certain voices, to the point where they'll read _anything_ that narrator works on regardless of the book's author or genre. If I had the budget for it, I'd definitely favor a well-known human narrator over AI for the visibility aspect of working with that person. But most authors don't have the budget to hire popular narrators, which is where less popular or entry-level narrators may find themselves losing work to AI alternatives. The narration quality is still higher with competent humans at this time as well, but that'll change.
For translations, I don't think I'll ever trust AI entirely (just like I don't trust myself as a human writer entirely!) I'd still be hiring a native-speaking human editor and proofreader if generating AI translations. Or more likely, I'd be hiring a human translator who is able to charge competitively by using AI in their workflows (and is also able to handle the quality checks etc for me).
