It would be easy to implement, but not all authors are going to implement such a system.
I think automatic disclosure of page of average words per page (AWP) and number of pages (NoP) on publishing should replace the current ranking system, which takes a great deal of time to get the hang of and reveals very little about the story.
Suppose someone is wanting to read something that will hold their attention for a long time, but can be read in short sessions. A lot of people don't just stop reading in the middle of the page. If the reader could see the number of words on a page and the number of pages, they could easily find a story that can be read in a large number of short sessions.
This is information that should be available to the readers of any story.