Import book metadata (my suggestion where user can directly add set of pages from his export list)
Export book metadata (export the book details containing all page links to a file which can be saved by user, similar to MetaBooks)
Add to a book option for every page
Table of contents for a book
Read a book
Recent changes for each book
Create chapters
Arrange order of pages in a book
Protect/watchlist/move/delete all pages of a book
List books
Search for a book
Search in a book
Automatic Bookshelves, where the books of a wiki could be organized according to their metadata (examples: English, Portuguese, ...). See also Book tool#Bookshelf.
Book specific CSS, JavaScript, and Gadgets
Automate categorization for chapters, pages, templates, and files
Book-level feedback, statistics, feeds
A more uniform and organized discussion system for each book
List all chapters, pages, templates, and files in a book
Book-level What links here for files, templates, and categories
Book-level link search
List all wanted pages, files and templates in a book
List all broken and double redirects in a book
List new pages in a book and new users who have begun contributing to a book
Goto a random book's main page or a random page in a specific book
Stable books
A way to view/read an entire book as it was at a specific point in time
A way to include additional information shown within book listings based on their meta data, and not just for sorting
Book, chapter, and page metadata
Allow book listings to be sorted and filtered by name, size, number of pages, and any other meta data
FULLBOOKNAME, BOOKNAME, CHAPTERNAME, and FULLCHAPTERNAME magic words