Yeah, 6.001 never covered the bulk of what the book covers.
Still, I think Scheme is sufficiently different from mainstream programming languages that it's... like teaching git to a crowd composed half of SVN power users and half of people who have never copied a folder to folder.old in their life. You're balancing teaching "oh, here's how Scheme's different" from "oh, here's how you should have thought about it all along".
In particular I remember the OO system being pretty confusing at first, since my background, from high school, was C++. It makes a lot of sense that Scheme gets out of your way and lets you implement a nifty OO system using just closures, but to someone who expects a language to treat objects as first-class and lambdas not, you're inevitably going to be trying to learn the SICP OO system by comparison to the C++ or Java one.
All that said, I'm not blaming the language at all. I think the quickest fix would have been for MIT to offer either a placement exam or voluntary registration for two classes, one for students who were more-or-less new to programming and one for students with a strong background in something like C++ or Java. Both classes could have used SICP as a text and worked fine.