Which means we are probably at least 5-10 years away from verifiable action that a court of law will recognize.

This assumes it's possible. I naively assume it's not, in a way that doesn't harm the model, beyond the content of the book.

Until you get models with completely disentangled feature spaces such that you know that the influence of a piece of data is completely removed (at the limit this is something like an embedding DB), there is absolutely no way you can claim you’ve removed the data from the model.

At most, these efforts will amount to data laundering where it will be impossible to prove that a piece of data was used to train the model, not provide conclusive proof that it was removed.