I haven't thought about that too much, because I try to be happy with what I have. But I will think about it now ...

I like how some reading apps allow you to adjust the screen brightness by swiping up and down the left edge of the screen.

Automatically going to library view instead of the home screen when tapping the home icon, and when restarting after a forced shutdown (i.e. holding the slider for a few seconds).

Automatically returning to the last page read when restarting after an automatic shutdown (i.e. when it turns off after a specified period activity).

Regions or gesture for next/previous chapter while reading a book.

I'm sure that there are other things that could make life a bit easier, but I spend most of my time within an individual book: reading then flipping pages, plus a definition or two.