John Tiffany: Jo Rowling was incredibly generous. I met her first, and I already had a soft spot for her because she used to write in the cafe of the Traverse Theater in Edinburgh when I was the director. It was only after the first book came out that I realized it had been her, nursing one cappuccino for four hours. When we met to talk about the play, she asked, “What do you think the Harry Potter stories are about?” I said, “Learning to deal with death and grief.” There was something in her eye — I thought, we didn’t say it’s about transformation or magic or flying on brooms, and we’re on the right track.
Thorne: We all met in Edinburgh and as the day developed, we knew we would take the epilogue of “Harry Potter and the Deathly Hallows” as a starting point.
Tiffany: All the seeds are there; we start with that scene in the train station. Am I allowed to say that? Anyway, it was clear that she was going to let us take those characters and have our own ideas.

Джон Тиффани - продюсер Проклятого дитя. Торн - соавтор.

Если вкратце, когда они работали над ПД, Ро спросила его, о чем же все истории о ГП, и он ответил, что они учат справляться со смертью и горем. Ну а дальше Ро этот ответ понравился и все завертелось.
Не знаю, насколько это все правда. В интервью они все очень гладкие и прилизанные.