When you read "rare books", what are you thinking these are? The 404 article that spun this story up goes into more detail. These are like vanity press books. They're rare because nobody cares about them. The book industry already destroys these books.
I am thinking about a long essay Icelandic author Þórbergur Þórðarson wrote to his pals abroad, and were left abroad. I am thinking about a photo book by an Indonesian naturalist who is famous on Bali, and took amazing photos of wildlife on Sulawesi in 1926, and colored in, and somehow ended up in New Jersey in the 1980s. I am thinking about a collection of essays written by a teenage J.D. Salinger who he left unsigned at a café thinking nobody would want to read them but just leaving it up to chance. Or maybe a Jackson Pollock sketchbook he lost at a party which ended in the host’s bookshelf, and finally at an estate sale.
Plenty of such unknown unknown exist, and the AI machine will inevitably destroy a bunch of them at this scale.