I haven’t properly researched whether Arianne Martell is permanently cut out of Game of Thrones, and honestly, I’m afraid to find out. It cannot happen. It cannot fucking happen. You cannot take out the amazing plotline that is Arianne and her birthright as Dorne’s heiress, the only woman in Westeros and possibly the entire world who expects to inherit the throne in her own right and before her own living brothers. You cannot cut out the plot that illustrates the equal primogeniture system that is a complete political anomaly and is the basis of Dorne’s very existence and comparatively progressive culture. Godfuckingdamnit.
In my mind, they’re doing this because they’re meshing Quentyn and Trystane into one character and Arianne will show up to inherit later, either as a younger child that becomes the eldest (this is not a spoiler, this is pure speculation—this is GoT after all, anything can happen) or is temporarily exiled slash barred from inheriting because she was up to her old shenanigans again. This has to be what happens right? They’re not going to give her up in favor of some fucking 12-year-old boy who barely appears in the books?