One thing that might make a difference is to have a count of comments below mine - I often check my own 'thread' and it would be useful to have something like "you made 6 comments made in past day, and people have left 14 sub comments, 3 in last 2 hours".

If I cared I could dive down and see where conversations were happening. as it is I really only spot a top couple.

I guess it's halfway between real state and ephemeral