Most of the internet and the people I've spoken with about it think it's a grab for cash on JK Rowling's part and they're pretty unimpressed about it. Yes, the film company does have dollar signs in their eyes. The Harry Potter generation has grown up and their kids are into the Hunger Games and Twilight. They want to re-capture their glory years. But I don't think JK Rowling is being involved in this to make more money for herself. She is richer than the Queen and the first author to become a billionare. She does not need anymore money. She has so much money she doesn't know what to do with it. She's donated a lot of it.
I think the reason JK Rowling is returning to her wizard world is because of her failed attempts to dip her toe into the world of adult fiction. Her first try, the Causal Vacancy, got terrible reviews because everyone thought it was going to be as fun and gripping as Harry Potter with lovable characters and a wonderful, rich world. It was the total opposite and people were disappointed. So JK tried again but under a pen name to get less judgement. Her book was a modest success...and then she was ratted out to the media and her book soared up the charts and she was swimming in cash that she did not want or even hoped would not get.
JK Rowling doesn't have to and doesn't want to write for money anymore. She writes for the enjoyment of it. She will never be able to escape the shadow of Harry Potter and I think she has come to peace with that. It makes sense then for her to go back to that world and flesh it out a bit more...I mean, why not? I think her decision to set the films 70 years before Harry was born is a great idea because it introduces us to a new time in the wizard world to explore. And having it in New York is going to be interesting too (I am curious if that part was her idea though and not pushed on her to capture the American market)
One of the things that made Harry Potter so delightful for me was its setting in England. I am interested in seeing American wizards and maybe even an American wizard school!