Willie, you've just landed on my MAJOR "what?, and why not???"
I've never understood why folks taking/getting single hander lessons aren't taught some of the basic spey casts.
The rod niether knows, nor cares, what kind of cast it's being asked to execute. Other than 'skill level' I can't think of a single "spey cast" that can't be done with a single hander.
Willie, a slight correction if I may. It was 'us' Canadian's that invented spey casting; we taught it to the Ammi's. The rest about them going to Scotland is probably correct. As a group, we're far too modest.