From the third season onward, the financial and symbolic future of Downton is constantly at risk. While it might seem a little repetitive to keep bringing the storyline back up, it's actually very true to life. After World War I, society changed enormously, and many aristocratic families found themselves facing challenges like higher inheritance taxes, the loss of heirs in the war, and changes in social priorities.
In reality, many aristocrats did lose their ancestral estates, while others had to massively adapt. The "film stars come to make a movie at Downton" plot in "Downton Abbey: A New Era" may sound silly, but it's one of many options that these landowners would have pursued to make enough money to stay. In fact, that's actually the story of Highclere Castle, where "Downton" is filmed! The castle, which has been a filming location as well as a tourist attraction, is the seat of the Earl of Carnavon — a family which fans of "The Crown" will recognise as the family of Queen Elizabeth II's horse racing pal Porchey.