Even bigger than that (I think at least) is the potential for fully voiced mods. There’s nothing stopping modders at that point from adding content indistinguishable from the base game.

I'd love to see that. Voice acting for mods where you want to include new NPCs requires either someone to donate some voice lines, or paying for it to be recorded. If you want to patch existing NPCs, that's even harder because getting the original voice actor to do the new lines would require both persuading them to do it, and complying with any agreements they might have with the publisher that could prevent that.

I doubt Bethesda would facilitate this. They'd likely use voice actors to train the voice, and having a famous voice actor saying saucy kink/bdsm/violent things that you tend to see in some mods wouldn't be great PR

How would the union take to that, though? This is not meant as an anti-union comment. I'd just be really surprised if Bethesda ever got to work with union VAs ever again if they went all in on an all-AI voiced game.

If they went all in on generated voices, would they want to work with voice actors?

I could see Bethesda still wanting to select voice actors to train the model with, especially if they're household names. So they'd get paid.

You do raise an interesting point, though. Compensation for AI-derived transformations of your work (in this case, your voice) needs to be a thing.