I love the threaded messages in the cards view but there is no indication that a new message has arrived in the thread unless you expand. Would be great if the card turned bold again to indicate there are new messages in the thread.
YES! I have the same problem or idea respectively. It IS a problem that a new email within a thread is not obvious. (Maybe the thread moves upwards with a new email in the thread, but what if other emails arrive, too? You will easily miss the new "threaded" email.)
Here's my suggestion: make the "arrow" (>) that indicates a thread BOLD as long as there are new or unread messages inside. If all the messages have been read, it will turn to, well, normal, thin, you get the idea.
I would love to post an image that I prepared, but I don't know how. Apparently you can only LINK to images. Well then, I hope the explanation will do.