I would like the functionality to add bookmarks to books! I can't believe there isn't just something to click on the top-right hand corner of the logos app for iPhone and iPad to add a bookmark. Sometimes, when I'm studying, I just want to see all the bookmarks I've made. I imagine this would be a simple addition.
I know some of you might suggest I use favorites/notes, but let me just say that they are considerably more unwieldy than what would be created by a bookmark paradigm. It can function similarly, but with unlimited bookmarks, a one tap-to-add solution, and searchable data to return to the information you want to remember later easily.