12.5 [over.built] paragraph 11 says,

For every quintuple (C1, C2, T, CV1, CV2), where C2 is a class type, C1 is the same type as C2 or is a derived class of C2, T is an effective object type or a function type, and CV1 and CV2 are cv-qualifier-seqs, there exist candidate operator functions of the form

CV12 T& operator->*(CV1 C1*, CV2 T C2::*);

where CV12 is the union of CV1 and CV2.

C1 and C2 should be effective class types (cf 7.6.4 [expr.mptr.oper] paragraph 3.

Also, should the relationship between those two classes be expressed as std::SameType or std::DerivedFrom requirements?