I meant more like when you re-open a thread you've read before and there are x new comments. It would be nice to have those comments highlighted so they're easy to find. Sorting by new works but only for top level comments.
I'm used to it coming from Sync for Reddit. See the green comments with dots:
I swear to God if someone gave me reddit and said, "make this thing profitable," I really don't think it'd be as hard as he seems to think it is.