I'm both pleased to learn about it and a bit disapointed it never happened.
It's interesting to see that they were going for this, while Kingdom hearts is also hinting on a Versus XIII reference.
In the end, a concept leaded to several project.
In this, i wonder if we would have gotten the good ol trashbag outfit, would have been a funny reference, still pleased that it appeared in Dissidia, now let me ask something, if it appeared in dissidia, was it because of episode Noctis being planed or is it just a reference? after all Lightning does have her Grey hair in 012 from original XIII concept.
I'm still curious, i think i'll always crave for more information between rumors and reality.
In a more personal note i always felt so attracted by Stella, I was sad when she got replaced, she had something, something pretty i was never able to find in Luna, In any case, it was a concept, we know now, that they had way more plan for the "heroine" whoever you call her Stella or Luna, and for some reasons they didn't managed to reach it.
With Dotf, i'm pleased to see that they really wanted to work on luna and her strong will, that saddly we will only see through concept art and a few lines.
FFXV is a truely interesting experience It's unstable, it have his bad and good things, i both blame and thanks nomura for showing it way too soon since i enjoy beta, well at this stage you can call it Alpha, Stuffs. And in the end despite being around for 10 years, the game was nothing but in dev for ~3 years, way too short for all the planed things. What is done is done, but we can't hide that a part that gave FFXV his unstable reputation was the promised things.
big thumbs up to the team who continued working on it after the release To be honest. Anyway, sorry for throwing some point of views ahah.