It will fully-implement NIP-62, and will probably be the first major client to do so. The books are actually complex constructs of Nostr events, not media files. That means that we can analyze the content and reuse the individual parts in other events, so that the parts are also traceable links, you can click through, to navigate between publications. We will also be using special source events, vector embeddings, and etc. in the Euler edition (nostr:npub1m3xdppkd0njmrqe2ma8a6ys39zvgp5k8u22mev8xsnqp4nh80srqhqa5sf is already tinkering around with that).
We will also be implementing a social layer (but not kind 01, we're avoiding that, like the plague) around the publications, including communities, book clubs, and rating systems.
Gutenberg is the MVP of the product, just to prove that you can use it to print and read an e-book, with hierarchical, replaceable notes. Which took almost 6 months of trial-and-error, to figure out, but which seems to be working well, now. The table of contents is being revamped, at the moment, but soon it'll reappear in the left-hand panel of the books.
https://github.com/nostr-protocol/nips/pull/1600
Also: