The Duffer brothers have (at least) been in talks with Steven King about a big-screen adaptation of the book "The Talisman". At the end of the last episode of season 4, Lucas is reading to Max in her hospital bed from "The Talisman". So, "The Talisman" is as likely as any (and, by the way, there are some significant similarities between "The Talisman" and Stranger Things).