History Playback
I think it'd be totally rad to have a version history playback feature similar to what Google Wave had back in the day. This way people could go back in time and see how the conversation led to changes in the context and proposals step by step.
A more visible way to track conversation development over time would be great and @alanna your vision sounds amazing! In the interim, there are small things coming up in the more immediate pipeline that I think make the process more visible.
I have been talking about this right from the start! Definitely want to see it happen someday! In my dreams, it's beautifully visualized, along with engagement statistics for the group. I have called it a "Decision Timeline" - imagine being able to see it laid out, and you could hover over dots on the timeline to pop up the decision there. I also have fantasies about a branching structure, where you could go back and revisit an old decision with new information or experience, make a different choice, and then track a different timeline. So groups could look back and say "OK when we decided X, we ended up here. When we went back and decided Y instead, we ended up in the other place" - they could really see the influence certain decisions had on their group's evolution and progress.