Here's my take: I think she drew inspiration from "Narnia" AND "The Magicians"...it's funny because the author of "The Magicians" literally used "Narnia" to create his story. The book "A Starless Sea" came from The Library which is located in the same universe as "The Magicians" (I think "Narnia" is also just another dimension of reality within ours it just takes place in the modern time with adults not children, which comes into play with "The Magicians"). Especially when she says some books require gloves to be held... just like the The Poison Room. It is literally a radioactive room with books that contain certain knowledge that could be dangerous if in the wrong hands. Essentially too dangerous to be in normal circulation. Like how there is a book written for every person to ever exist....kinda like how Zachary basically found a book that is sort of a part of his story. Of course there are individual stories for each perspective and these timelines will overlap and be in other books.. the painting of the door to The Starless Sea, the Clock to Fillory, the wardrobe to Narnia. So to me, this book is extremely nostalgic for these other stories... about the wonder and magic of the world of imagination! I'm positive that this was what she was trying to share with us. Another thing I thought of... "Sweet Sorrows" is only one volume of many. "The Night Circus" is just one of the stories in this endless story of stories. Ingersoll Lockwood wrote fictional books about Baron Trump and his dog Bulger. They discover a book that describes an inner World within the Earth connected through tunnels and there are civilizations there. There's also time travel, but mostly it's about A World Within A World.
As much as I love The Starless Sea, it feels un-adaptable into a movie. There's just so much in it about the love of books that it would be like reading the script to a documentary about filmmaking. The Night Circus is adaptable, but I'm not so sure about The Starless Sea.
For the first time, after looking up forums, reviews and so much more. Finally I found someone who understood the book the way I did. Hey there, fellow dreamer.