It’s not unknown. ITS COMPLETELY LEGAL. 14CFR part 380 if memory serves. The public exemption charter has been around for years. I worked for a 135 outfit that did the same thing JSX is doing back in 2011 flying 2x a day between TTN and BED selling 99$ seats. The FAA ramped us every other day or so, but never once found an issue. You could sense they didn’t care for it but they also knew it was legal, and said as much. We spent our 10 minutes together, shook hands and went on our way. In the end the business model failed, the subsidiary closed and we moved on to strictly charter until becoming a 121 carrier. Seems like JSX has figured out how to make the model work better than they did.

https://en.wikipedia.org/wiki/Streamline_Air