I have never heard of such a speciality, but it doesn't seem like such an off the wall idea. The drawback would be the complexity of such a speciality. Most diseases have strong genetic components. It could be a speciality within a speciality. I guess as an internist, one could deal specifically with the clinical coordination of new genetics based therapies.
As for genetic counseling, the field is blossoming. Most programs are catering to granting MS degrees. I guess as a physician working with genetic-based diseases, it would be a nice perspective to offer to patients.