Right, I think the time has come for a resume of known story facts (from a development standpoint):
* The original script draft was written by Kazushige Nojima (FFVII/VIII/X/X-2), while the current script was written by Saori Itamuro (of Dissidia fame).
* XV, in its original Versus form, was intended as a multi-game storyline. The current version has been adjusted to fit into a single game, with additional media to help communicate the finer detail or major story elements that wouldn't fit in very well.
* The game is divided into fifteen chapters, excluding the "Chapter 0" prologue.
* Despite the use of dialogue choices, there won't be alternate endings, or a cliffhanger ending. It will be a single, standalone story experience (sans DLC).
* The lore is based on Fabula Nova Crystallis and retains its themes, but all terminology and related marketing material has been removed, and it has been augmented with additional elements, allowing it to stand alone or be a distant cousin based on your preference.