I found your proposal interesting as I have been thinking of something similar. What i was thinking is that any nodes underneath a reaped node become "dead nodes". That is they can't be replied to, they can't be voted on and they wouldn't show up in worst nodes or in any of the node lists like NN or RAT or the like.

The point would be to cool heated threads, and reduce the "snowball" effect of a troll and those who feed them.