@Idolse: have you gotten around to this yet? I think that a user initiated counting process which updated a custom column is a good solution. As of now I use an unholy shell incantation which relies on wc and the book existing in txt format to do exactly this, but I'd be interested in a plugin which handled it for me
I'm no python coder, but if there is anything I can do to help let me know.
If anyone's interested in the shell script I can share it, but I wouldn't recommend it for production use (horned bipedals might show up on your door).