I think that one feature which would be useful to add would be similar to the ‘percent read’ feature on a ebook, that tells you your current position within the text that you are working on.
This could be useful for a variety of applications, including editing and outlining, to see if your midpoint happens at about the halfway mark in your manuscript, or to check how far along you are getting as you edit from the beginning. It could be a simple metric that always displays at the bottom, or something similar to the word count box which can be pulled up at will.
