I'm interested in getting a few interested people together to talk about possible solutions for viewing diffs (including previewing changes) and handling edit conflicts for VisualEditor.
We don't need to do anything formal really - if you are particularly interested in getting involved let me know. If there are a few of us I will throw a short brainstorming session together and we can go from there.
Just to throw something out there to give you a feel for what little we have considered in this area: it is possible to utilize the granular history data we capture for undo/redo purposes to support playback. This would give the user a time-slider that takes the document from one state to another, and a play button to animate between these states. This is usually considered to be a "cool" idea, but we don't know that it's practical or respectful enough of people's privacy.
I think this is an exciting area of VisualEditor with few restrictions and almost no existing ideas or plans, which makes it possible for us to come up with radical solutions and make them a reality.