Seems like it's bigger than I expected. The full index doesn't show, but it's at least 10 pages, and it's more than just scrapped contents. Seems there's a lot of recapping of Roger's life, and the mystery of the last Road Poneglyph (I found it weird they put a focus on it, since I don't think it's been addressed inside the story).
The book lists three possible locations for the last Poneglyph:
Of course it's not saying it has to be in one of these, but I find it very, very interesting that Vira is singled out like this, next to two really important islands.
Also, we are getting a Rocks recap, so we may get new information.