There’s a couple of bits of the book which are err ‘problematic’ and I suspect won’t be included in any movie.
The central idea of the book is brilliant, but the ending did feel a bit unsatisfying when I re-read it recently.
TBH King’s a bit like Philip K Dick- lots of great ideas to plunder but mostly you don’t want to actually make the film of the book.
People seem very upset about this with Dark Tower but since it’s pretty much unfilmable and a pretty good proportion of that series is absolute ****, I’m OK with that. It’s a brilliant core idea but it’s all over the shop. In the case of IT, if they make it more like the book and less like the original film people will complain, you can’t win.