I was going through the comments on the submission: Re-Designing the classic email client (vanschneider.com), and most of the comments add nothing to the discussion.
I thought a good approach would be if a comment in the discussion went sour then that and its descendants gray out, as any child comment is just off topic any way.
I am thinking the end result will be all relevant comments available to engage with. It would also discourage commenting in a grayed out tree for obvious reasons.