This is excellent news because it means that folks who pay for printed books and scan them also can train with their content. It's been said already that we've already trained on "the entire (public) internet." Printed books still hold a wealth of knowledge that could be useful in training models. And cheap, otherwise unwanted copies make great fodder for "destructive" scanning where you cut the spine off and feed it to a page scanner. There are online services that offer just that.