Unadded Excerpts is a great idea so we can customize the Mindmap without creating extraneous notes, but it’s not very usable. If you have more than one or two, when you try to zoom out in the Unadded Excerpts window, the view shifts and excerpts disappear. When you move one to the mindmap, the mindmap shifts to somewhere, and it’s impossible to find the excerpt you just dragged.
Maybe a small Unadded Excerpts window (draggable lists) would work better. If the drag and drop to Mindmap can’t be improved, a simple menu item on the excerpt itself that says “Add to Mindmap” which drops it in the middle of the current view of the mind map would work great. It would also be great if Unadded Excerpts included the document name and headings somewhere on the card.