Some interesting leaks about FFXV's development and it's roots as Versus XIII came to light today.
You can be at ease and read further since they are not going to spoil anything of the actual game and it's story.

The information comes from a guy who also knew about Iris (Gladio's sister) and the DLC plans ahead of time, so his information seems legit.
He says that fans have been romanticizing Versus XIII and Stella's role. Versus XIII was mostly just a very rough concept by Nomura and some fancy cutscenes especially produced to be presented as trailers and Stella wasn't really fleshed out either. They scrapped her pretty early and replaced her with Luna as they reworked the story and noticed Stella only had little space and just didn't work out.
In 2010 there existed a demo of the game behind closed doors that was really poorly received. Nomura seemed to have bitten off more than he could chew and after some years the director's job was passed onto Tabata (announced in 2014) who is known for his pragmatic and straightforward approach.
When Nomura still worked on the game they actually were planning 3 different games (just what Nomura is planning to do with the FFVII Remake). The games were supposed to be 20-25 hours long. What we get now is a merger of those three games.
No offense to Nomura, lol, but he should rather stick with being a character designer. XD He seems to be a major pain the ass for Square Enix. His other works as a director include the Advent Children movie and the Kindgdom Hearts series which is infamous for being convoluted and split into an unnecessary multitude of titles, including Kingdom Hearts 3 which is for many years stuck in development hell. Now he is working on the FFVII Remake series. Doesn't sound too good if you ask me...