But I think there’s some neat ways of starting with the more familiar — e.g. flowcharts — and using those as a start for a storyboard. So in effect, a storyboard can be shown literally above the storyboard, where certain sections of the storyboard could visually line up with sections of the flowchart. Worth a try?

One, I believe in the effectiveness of storyboarding in UX. However I think as UX practitioners we often abandon the technique prematurely for more familiar means of communicating design like flowcharts, screen mocks, presentations due to the fact that ironically lot of designers are afraid to draw!

Second, I agree with your notion that clients typically are not conceptual thinkers like us and storytelling is lot more resonant with non-designers however engineers and product managers in cross-functional teams do get flowcharts and diagrams. In some ways, UX design artifacts share similar characteristics as engineering artifacts like use cases and flowcharts.