Currently, if there is some discussion in code and the revision is updated the comments from the previous revision are hidden from the top level UI - you have to navigate to the table of contents and click on the link for the inline comment to open the diff in a separate window. This makes it very hard to see the full extent of the review after it is completed if there was some iteration (because most of the comments will be hidden either by collapsed table of contents or by the newest revision). It also makes it hard to iterate, especially if there is more than one place in code being commented on per file. Consider the following scenario:
1. Author submits a review
2. Reviewer makes some lengthy comments on line 1 and line 10 of some file and requests some changes for both. A lengthy discussion follows in both places
3. Author comments back with something like "let me work on the first one and see if we can get it right".
4. Author submits a new diff with changes to address comments from line 1, but leaves line 10 unchanged.
Now the discussion on the second point is broken up across revisions and there is no way at all to see it fully.
This seems like a corner case, but actually happens quite a bit with reviews that have a couple of small issues and a larger more contentious issue where more discussion or clarification is needed, and in this kind of scenario it's the more complex issue that ends up being broken up,
It would be awesome if updating a revision could keep the threaded comments visible and figure out what line they moved to, if necessary. Obviously there's some corner cases here (like undoing the entire change being commented on), but even getting this somewhat working would make the view so much more comprehensive.