I mostly use Poweramp to listen for audiobooks. Trying a lot of other audiobook-oriented players I found Poweramp is really perfect and most stable one. But it will be nice if few features extremaly useful for book listening will be implemented.
Not sure these features were not requested but I did not found them here So please forgive me if I'm repeating...
First and most anticipated one is 10 second rewind using headset button. Poweramp already can jump next/previous track using headset button but it would be beautiful if user can choose action to perform on each button event individually (including 10 seconds rewind)
Another feature is just an extention of previous one: auto-rewind track after pause. The seek back time could depend on how long listening pause was. E.g. it may be 10 second if playback was paused for more than 1 minute and 30 seconds if audiobook was paused for an hour or more.
And last feature many audiobook players have is a "book-based" seek bar. You may view/change playback position not for current fragment (track) only but for whole book (folder).