If they reproduce their results in other clinical settings, the immediate impact on patient care includes: 1) accelerating diagnosis (and treatment) for patients with traumatic brain injuries (by effectively up-scaling lower resolution scans) 2) healthcare providers in developing countries will effectively get a low-cost "upgrade" to their existing equipment 3) cancer patients in rural America could be monitored for treatment response in a setting that is closer to home (because rural communities tend to be resource-poor in terms of medical technology).
If we consider that a logical extension of their work could be to develop a compression algorithm for MRI data, then it's easy to see an even broader impact that includes: 1) connecting rural patients with high-quality radiologist services (i.e. remote MRI interpretations), and 2) decrease the cost of long-term storage, access, and retrieval for MRI data.
On the topic of FB's issues with privacy: I agree that FB has a long way to earn my trust as a doctor and a patient. That being said, it's important to give credit where credit is due. It seems that FB gained access to the imaging data by working collaboratively with NYU on this specific project. By comparison, it's an open secret among those of us in the biomedical informatics community that over the course of many years Google Cloud has quietly gained access to the personal health information of millions of Americans. So, when it comes to privacy concerns, it's important to avoid being myopic - the concern is valid, but the primary threat may not be as obvious as it first seems.