Comment by ChuckMcM

Posts is an interesting alternative. It has the same verb/noun flexibility as comments. But really it is minor, I wondered what 'stories' was but quickly realized it was things that I had submitted. So I think you should keep what ever you feel is best.

Given that you know "when" a thread was collapsed and you know when a given comment was added, there is data available to compute "new since you collapsed it" but I recognize that would an interesting challenge. So you keep the comments in a list, and the list can be internally sorted in date or karma order, then sorting by date you could splice it at the date it was collapsed and compute the length of the two lists (pre-collapse and post-collapse). I have no idea how useful that is, just collapsing huge threads (especially ones that wander off topic) is such a huge win.