Hopefully I have interpreted your request properly

A) The discussion board is helpful to those who organize the class in that they can organize discussions according to a timeline. This linear structure allows us to access discussions according to week.
B) BUT--once a discussion is in the past, it is swallowed up and if you want to go back to something a participant said and reconsider it, it is hard to do without wading through a bunch of other stuff. In a mooc with so many participants it gets overwhelming.
C) I think being able to tag posts and access them through a tag cloud would be helpful