I would like to be able to place a marker in the timeline to visually annotate a point in the history where I might have to rollback to in the future. For example, to mark the correct point to go back to before a mirror operation to capture all changes. This would be a line with an outlined pointer at the top which you can mouseover to reveal the title and description of the milestone. See mockup below..
Another idea in IdeaStation asks for the ability to add comments to operations as well as rename them:
https://forums.autodesk.com/t5/fusion-360-ideastation/annotating-events-on-timeline/idi-p/8986685
I would argue this might be a more streamlined way of doing the same, while also providing a visual marker in the timeline for the comment/milestone.