I made a little progress on this, will keep looking at it.
As you'd said, I used dual axis and the Gantt Bars.
Marked the Minimum CI, made a height (Max-Min) and put that on Size Shelf.
Played around with transparency of colors because of overlap of bars.
Couldn't get the tops and bottoms marked off, though.
Maybe something could be done with Shapes.
confidenceintervals2.twbx 24.4 KB