There are at least some Duolingo courses that use AI voices exclusively and they are shit.
On the one hand, having an AI to talk to sounds like something that could be good. Getting a real person to talk to every user would be impossible. I just don’t think the technology is going to meet expectations any time soon.
The problem is if the user asks the AI a question about the language they're learning they'll often get confident bullshit as the response and they won't know it's wrong because they're still learning.