The DLC seems to reutilize concepts that didn't make it to the full game, like Ignis reusing certain things from the planned Leviathan sequence (running across rooftops) and it definitely seems like the wintery environment lighting is at play, but the coincidence between FFXIII-2's dream sequence and the fact that Prompto was facing the same crisis as Noel and Serah, in that he has to affirm his identity and who he is before he can move forward, although due to XV's realistic nature it's more of an actual dream than the lucid dream Serah and Noel have.
For something to be a coincidence, it needs to be unlikely that it would have arisen similarly in both places on their own. Using a dream to literalize a character's need to affirm their identity in order to move forward is quite common in fictional works that are interested in human psychology; there would have been plenty of motivation for XV to advance Prompto's character arc that way in the absence of any FNC influence.
With the Luna bit, Stella's role expanding definitely was part of the plot change, as it's a given that Kingsglaive repurposes the original invasion plot for the movie and also presumably applies some of the things Noctis and his friends did to Nyx and his friends. Given the way Luna seemed ready to put on the ring, it's plausible in the original draft of Versus, Stella was meant to die before the invasion ended and was the one to use the ring for the old wall, leading to her death and "Noctis" being responsible, as he never put it on as the new rightful king of Lucis.
If you're going to pull the potential leak about Noct being responsible for Stella's death into this, it seems kind of disingenuous to leave out the fact that the same leak heavily implied that Noct actively
killed Stella.
For what it's worth, I don't think the Old Wall existed in Versus. There's concept art of the destruction of Insomnia in Versus, and there are giant Reapers that appear to have played the exact role that the Old Wall does in Kingsglaive:
As such, it seems pretty clear to me that the Old Wall was developed as a means by which to give House Caelum a connection to death that was less likely to cause problems with certain ratings boards.
Clearly, this idea sounds too small and Luna was likely to go the way of Serah in XIII-1, being taken away early on in the adventure and then being used as a lure to bring the l'Cie/Lucian King towards their destiny. Even the way Luna was to take on Ardyn's role in DotF, that was probably her original purpose to begin with, but they explored her character more, evolving from the love interest that dies early on and then resurrected to fight Nocto at the end, she developed into Luna, and with Luna's ties to the gods, the gods themselves became more important in Nomura's iteration of Versus XIII when he tried to have a trilogy. Given the FNC-related games have scenarios developed alongside one another interpreting the same broad strokes FNC story, looking at XIII as a solo game and as a trilogy and Type-0 can help identify some of the broad strokes that got snipped from XV.
I don't see Stella's role being anything like that, given the various leaks (of admittedly varying plausibility) about what she was meant to be. If Stella was connected to the FNC gods, it makes
far more sense for her to have been connected to Etro than to Bhunivelze, especially since the final game ended up connecting
Luna to the obviously-Etro logo.
Also, it's vital to remember that XV's gods
were not Versus' gods. Versus' gods were FNC gods; summons like Bahamut were nothing more than the standard "phantom beast" entities in Versus:
There was an old chapter list leaked with the big datamine, listing the original Chapter 15 as Trial of Bahamut. This is the earliest chapter listing it seems, and represents the original scope of the game. A Trial of Titan, a Trial of Leviathan, both revolving around stopping Nilfheim soldiers and breaking the machines tethered to them. Titan was originally supposed to join your side and you'd fight the army; this was presumably when Safay Roth was an antagonist and leading an army to kill the gods. Leviathan featured trying to free Leviathan, climb tanks, and do things with Prompto like we saw in the original 2013 pre-viz trailer where they're evading water dragons and soldiers. Then Trial of Ramuh seems like it was as intended but they never wrote anything for Ravus to do, as it seems like it was intended for Safay Roth to pursue you (it seems like that fake Cor execution storyline would take place here, hence why the chapter is so short). Trial of Shiva was meant to be a full dungeon, cut late apparently for reasons unknown (presumably for pacing as other parts of Terraverde got cut so the Shiva dungeon would be out of place) and was reinserted into Pocket Edition alongside the Leviathan tank section.
I mean, I don't doubt what's been revealed about the extended Titan and Leviathan setpieces, or that there was supposed to be a Shiva dungeon that got cut... but none of that really says anything about Bahamut. =P
(Also, "Safay Roth" is a terrible romanization of what I'm sure was meant as a more subtle homage - Saffirus, maybe? Sapphirus makes the most sense, but it doesn't explain the SAF, so switching out the ph for f is the easiest way to go.)
Trial of Bahamut... why do you think Comrades featured the Glaives being tested by Bahamut?
Because the devs wanted to end Comrades with an awesome Bahamut fight? Bahamut's actions in Comrades are as far removed from DotF Bahamut as they could possibly get -- given that he was forcing traitorous Glaives to do penance for their treachery to House Caelum, he actually seemed to take a willingly subordinate role to the humans who he empowered.
Why the Omen trailer makes the crystal so ominous?
Because it was admittedly made by a team that had been given limited information about what FFXV actually was for the purpose of having a cool concept trailer made?
Why the theme of the gods being awful in the FNC being gone here? It's because they ran out of time to develop the true ending where you prove to Bahamut what you are and pick your destiny.
Or, alternatively, because Tabata decided to disentangle XV from FNC and replace the FNC gods with a completely different (and less aggressively awful) pantheon.
"Live as a Man/King/God" and the three Florence and the Machine songs, these were likely composed early on when they had scope. Then as the end of 2015 came in, they knew that they couldn't fluff out Terraverde even though they started construction on the town outside Cartanica, and cut everything that slowed the pacing to the Crystal. Once Bahamut was snipped as the one preventing Noctis from choosing his destiny, we had to focus on what was there, i.e. Ardyn and his feud with Lucis and Luna. Luna, however, had her logo-role removed with Bahamut's removal, so they focused on her relationship with Noctis, the tragedy of her destiny and way she aids Noctis in his quest. With that we likely had the parallels to Ardyn with Aera and Somnus conceived in development, but even then, they realized they couldn't touch the 2000 years ago stuff so the Somnus blood feud was merely background and not detailed at all, Aera was hidden and the meaning behind Ardyn stabbing Luna and taunting Noctis at the end the way he does remains a mystery (like why Ardyn wanted Noct to feel powerless watching his beloved die). Then they had to focus on Noctis and his bros vs. Ardyn... but they couldn't cut Ardyn anymore as they wrestled with the Leviathan bossfight, graphics and just time itself so the bros got cut, snipping Verstael, Ravus and the history of the shields of Lucis. Then they figured they'd leave the hints of their DLC in the game... but that got cut too, becoming the Brotherhood anime. The snipped original chapter 13 where you wander the Forest of Memories in the Crystal was going to showcase a "A memory hidden deep in Noctis's mind", which was the story of Platinum demo and the Marelith fight most likely, and the memories of Luna was all of Luna's cutscenes; this got turned into Platinum demo, Luna scenes scattered and Marelith was once again attached to Brotherhood. Even Ardyn DLC, they couldn't do it all and put large chunks of it in the anime, and the DLC itself has various "cutscenes" that are slideshows once again indicating that proper cutscenes and gameplay was snipped due to time.
Again, you're assuming that elements that didn't even exist in 2016 were actually part of Versus. There's literally no reason to think that Somnus and Aera existed as characters prior to the development of Episode Ardyn. Ardyn's draft explanation of why Lucis' special color was black certainly didn't match up very well to the portrayal of his history in Episode Ardyn.
I also think that you need to consider whether something could easily be restored when positing its existence prior to cuts. If a Marilith fight had been in
any stage of development, there would have been no reason for it not to have been completed and added as free DLC, just like the Melusine fight that was added in a free patch.
(I do find the three endings/three FatM songs theory compelling... but it doesn't really require Bahamut to be an awful villain so much as Noct simply
finding an alternate way forward.)
Bahamut was always the villain... but the more they cut the story, the more the direction had to change so they could emphasize the story that is there. All that was left was the tale of Noctis being beaten up by the world, led to his death and us the player as well being tricked into believing this was good, when the truth is we helped Bahamut obliterate everything like Bhunivelze resetting the world. Even the way Noctis and Lightning were supposed to become the "True King"/"Goddess of Death" and then being replaced by their immortal former enemy who takes this destiny and vanishes into nothing. Honestly, just look at XIII for parallels to XV and the DLC as well as cut content. Even the Pitioss Dungeon has remnants of Ardyn's depiction of Adagium in those red statues.
So here's the million dollar question:
If Tabata had always intended the current ending to be a world-endingly bad ending... why keep that one instead of the supposed "good ending?" The devs were the ones who got to decide what to preserve and what to cut; while the current ending might be the only one that would make sense given the other pruning choices the dev team had made, it's kind of absurd to ignore the fact that the dev team probably wouldn't have made the same choices had they been aiming for a different ending.
My own three-ending theory makes a lot more sense of Tabata's ultimate choice for what to cut: essentially, only
two of the endings would be available from the outset, with the third only being available as an alternate-universe option on a second playthrough Episode Ignis-style. That way, there'd be a bad ending ("become a god"), a true ending ("become a king"), and a questionably-canon happy ending ("become a human being"), and the ending that was preserved was the most important one to keep.
EDIT: By the way, another massive problem with your theory about the three endings is that -- not only would it be much stranger to have two equally bad endings and a good ending rather than a bad ending, a standard ending, and a 100% ending -- that pattern of endings doesn't actually match the three FatM songs! I Will Be is bittersweet but ultimately hopeful ("And silence will not cover me"), Too Much Is Never Enough is clearly about making a sacrifice much like the one in the canon ending, and Stand by Me is obviously the happy ending.
Basically answered most of this in my above post, but I have to reiterate that yeah the gods got more important. They were before as fal'Cie, but with Nomura giving Stella a larger role, the gods took on larger roles. With Tabata keeping Luna and trying to keep the scope, they kept their importance but their context thru Luna, Somnus, Aera and other characters got removed for time.
Again, I think you've put the cart before the horse with regards to characters like Somnus, Aera, and DotF!Luna.
I do love the game. However I still think that it would have been bigger than VII and toppled the rest of the franchise had it come out full scope. True fans can appreciate the story, the scope, the game and more but most regular gamers haven't even touched the DLC, let alone the movie, anime and novels. It all could have fit had SE let them develop for 6 years instead of 3; they made bank on day 1, a truly complete XV would have outsold the rest of the franchise and would probably be looked upon favourably. All DLC could have been crossovers only instead of fixing and adding content we should have had. I love XV, but it's still a bit sad. With PS5 tech, XV would have never had development problems and could have tanked the original Leviathan fight.
Consoles will never be powerful enough to avoid devs biting off more than they can chew.
And I think we're just going to have to agree to disagree about what would have happened had XV come out as intended at some earlier point, because there's no evidence as to what would have happened either way. Given what Roberto Ferrari said about the instability of Versus XIII during his final year or so with the project, I'm not inclined to think there was
ever a solid plan for Versus XIII/XV right up until the game went gold.
