Off the top of my head, this needs:

Table of Contents support with working links; per-user storable bookmarks; font and color control; margin control; multiple methods of page turning; a non-bookshelf library index (I have over a thousand authors, most of whom have more than one book -- any interface needs to be usable by someone with a library of ten thousand books); and probably a partridge in a pear tree.

But it looks like a good core on which to build.