This isn't fan fiction, but I don't know where else to place this idea.
My favorite children's fantasy novel always has been and always will be Jane Langton's 1962 novel "The Diamond in the Window." I read it for the first time in fourth grade (1970? 1971?) and I still reread it periodically. To me it is Harry Potter and Twilight and Artemis Fowl and Stephen King and Anne Rice and everything else.
It's never been made into a movie, and I don't know if anyone has ever even purchased the rights to it. I think it is something John could produce. I also think he could have a small part as Trebor Nosnibor. The other reason is because of Eddie's backwards English.
The book is still in print if you want to look it up. Once you read it you will understand my comments about Trebor Nosnibor and the backwards English!

Mary