Thanks for your question. To be totally honest, I don't know. My work is predominantly in oncology and neurology, so I'm not sure what, specifically, is meant by "regenerative treatment." You can review Big Brother's definition of 'drug' in 21USC321(g). As I'm sure you're aware, not all drugs are created equal, and some are subject to additional standards (e.g., biologic products under 42USC262).
In any event, I don't recall the article indicating that progressive approval would apply solely to efforts within the field of regenerative medicine, and if I'm being honest, I'm not interested in limiting discussion to that specific topic.
edit: typo correction CFR->USC for drug definition.