Yeah, I was thinking vaguely of something along those lines as well. But I don't think using -$NORM is quite what we want, because that would mean that as the average node "quality" goes up, we become even more tolerant of even worse nodes. Instead, how about maybe something like -20 + $NORM. That would result in a threshold of -10.3 today. To put this in context: such a threshold would result in having no nodes posted today hidden, but all of this week's worst nodes of the week hidden (and then some).
I reckon we are the only monastery ever to have a dungeon stuffed with 16,