One UI improvement I would love is to see the number of unread 
emails in a thread in notmuch-show view. I often reply to a 
mail in a thread just to see that there are followup mails that 
resolve the issue already.

If I had seen that there are more unread mails in that thread 
(or at least that branch of the thread), I would read those first 
before hitting reply.

What do others think?

Sebastian