I agree with you - I think this is roughly the right idea, I just hadn't found namespace-undefine-variable! when I asked this question.
I think there's still somewhat of a problem with wrapping variables in a "let" with their deep copies - that prevents internal code from wrapping builtins and having other builtins use the wrap, because the let will make the builtin-wrap scope different from the outer scope. But you can do the special-suffix thing in this case.
