Working with long threaded discussions is cumbersome. There have been many ideas to improve discussions, but I hope this small modification would make a significant improvement when working with threads.
It would make it easier for users if the blue expand/collapse thread arrow were permanently visible at the top of each thread. (Ref.  in image below, image taken from How do I view and sort discussion replies as an instructor?.) Currently the user has to hover the mouse pointer over the area to make it appear. Without reading the documentation, who would know to do that? Currently we have to teach each new student (and instructor) how to expand and collapse threads. It is easy to forget this feature is there because there is no visible cue, so it's frustrating if you mistakenly click on the poster's name by mistake.
This is particularly important when in collapsed replies view, which is great for seeing the threads in orderly fashion. Collapsed replies makes a good overview of the threads, and the only way to see how many replies there are to each thread. (It's useful to tell students to use the first short sentence of a new thread to be the descriptive "subject" of the thread so it will appear in collapsed replies view.)
Especially in a heavily threaded long discussion, for example a tech support discussion, each thread really is a new topic. Students and teachers might want to quickly scan threads to see if their question is already asked (or answered.) In collapsed replies view, when students accidentally click on a the poster's name instead of the hidden arrow, they will be taken to the user's profile page. Clicking the browser's back button returns them to the discussion which is no longer collapsed and they are back at the top of the page. In the image below, the only thing that appears to be a link is the poster's name, so it's an all too easy mistake to make as you can see.
For teachers, if the student context card feature is not turned on, clicking on the poster's name by mistake has the same affect as for students; they go to the user's profile page. A benefit for teachers, that if the context card does come up you remain on the discussion page and don't have to start over. It has saved me many a time, but students don't have that safety net.