> why isn't there a strict "sane C++" or "orthodox C++" subset available as a custom language or compiler option yet?

Probably because sanity is (1) subjective, (2) in this case doesn't really come from disabling features (restricting language). He is still using most of the C++ features (overloads, operator overloading, templates) but only in semantic context that is obvious for them (i.e. templates for collections, overloaded operators for vectors and matrices). Therefore it might be a little bit hard to create a compiler front end that would understand which class acts as a collection or whether given structure is implementation of well known mathematical concept.