Yes the core of the contribution is the threading mechanism. Writing a low-level integration of CPython and $SCHEME is not trivial, but any implementer can do i

Yes the core of the contribution is the threading mechanism. Writing a low-level integration of CPython and $SCHEME is not trivial, but any implementer can do it. The syntactic interface we have clearly separates Scheme and Python code and we don't have to have new semantics for e.g. method accessors (you just write them as you would in Python).