Basic use of scheme requires you to think recursively. If you have that, scheme gives enormous power for a small investment of learning, thinking and typing. If you don't have that, you need to deal with that before you can use scheme.

You could take a group of elite students with a math/physics background and have some confidence that their grounding in mathematics and physics will have prepared them, or that it will be a short and healthy jump for them.

But it would be bigger hurdle for other groups. Python is a useful because you can ease people into this kind of thinking. And people who aren't there yet can still get things done.

Regarding SICP, even in early chapters, it requires you to understand maths concepts that wouldn't be available to you even if you were a professionally-employed person returning to to university. The Little Schemer path would be a better intro for groups without that.