[As a layperson] the most convincing argument the Authors Guild makes is given I think in their SCOTUS petition: that Google's "fair use" is sidestepping a legitimate business opportunity for the rights holders. Books are not just the paper they're printed on, and authors already as a matter of course hold the rights to plays, movies, etc adapted from the text. Particularly when there is no new expression, it seems to me you are just getting away with not licensing the data. This argument is one of the least-covered in the briefs, however. So.

If I were to make a bar bet, based on my limited knowledge, I would say that any bolder attempt to use mass digitized books for a "transformative purpose" like a chatbot or AI would not pass scrutiny (which kinda sucks, because that would be awesome). That's what I mean by overturned -- perhaps the current GB usage is fine because of point 2) above.

Of course, like many Court issues, the best solution (as yohui alludes above) seems to be to have Congress fix things with real law, such as to create compulsory licensing scheme like in music.