As I understand it the Ryanair pilots won their earlier tax case in Germany. So at least they did not get done for large amounts of back tax, which seems fair given there was genuine doubt about what was due.
Subsequently I heard the loophole was closed and that they were now expected to pay going forward, which does not seem unreasonable given that everyone else living in Germany is expected to pay tax.
What is clear is that the taxman in Germany has started to focus on pilots and not just Ryanair pilots. There have been similar cases with people in the sandpit who really were not living in Germany. One guy said he had separated from his wife, who lived in their house in Germany. But photos showed them on holiday together. He had to pay up.
So the word is if you are in Germany be careful, which in most cases means you need professional advice (e.g. a Steuerberater). I know this is not what most people want to hear. But I hope it stops people planning unrealistically and ending up with bigger problems later.