There seem to be 5-15 running on YouTube at any given time. And as far as I can tell this has been happening non stop for the past ~2 years.

Well, there are 25 running right now! D:

I think what just happened to the high scores is an accurate representation of what happens to half the things that end up on Hacker News!

You can get a rough overview of the changes per minute looking at https://codepen.io/Krinkle/full/BwEKgW which listens to the event stream. (scroll to the bottom of the page, its seems slightly broken right now)

This shows ~300 edits per minute on en.wikipedia (5 a second) right now. ~1500 edits per minuites on all sites (25 a second)