I graze the “Unread” page in a forum every few days for threads I subscribe to and “New” firehose-style to see if I can contribute.
It would speed up the time necessary to expand / unpack the new entries in a thread that I haven’t read yet in the full page instead of opening each thread each.
I’m aware this is more costly on the database to denormalize from the list of threads with new items to their full contents. To alleviate this you could paginate the expansion as in the current scroll behaviour and do it in batches if there are more than 10 items.
I searched the discourse forum with “full text”, “full post” and “expand” to get similar feature requests that want speedier read-time: