I really wish, instead (or in addition), that there was a "new" indicator so that I could quickly see recent comments. This won't do a late comer any good as all posts appear as new, but for those engaged in the thread, it would help them be able to scan and read any new comments since they last visited.

And/or indicate posts made in the past X minutes.

Maybe these could be toggle options to quickly show/hide or just shrink/lighten to the background older/read posts.

This is something I've been wanting since day one, but may impact performance too much, unless they handled the indicators/toggle client-side based on a last read timestamp cookie (or similar implementation).