I hope we start having interviews that clarifies things.
Because with what it's been anounced it seem's like 2018 is going to be the year of multiplayer and mods. Having to wait for a re-release of the game with new content that may not have the main story improvement that we wanted.
One thing i can imagine it's having a hard mode patch when the dlcs come so we can replay the game.
Something cool i could like about the alternate ending is about rebeling against fate and losing. Like in one of Mass Effect 3 endings.
Learning about Ardyn's past from the hand of Bahamut, give us the choice of Noctis siding against the astrals and the Cristal, using Umbra to change the past.
Noctis goes to Insomnia before the invasion, with the intention of getting what we can see in the image of everyone happy ever after.
But he can't save Regis and sees him die(like in the picture of one of the Artbooks), then tries to save Luna but he' s manipulated by the cristal so he kills her (so she can still fullfil her role as Oracle) in the same way Ardyn used his magic to trick him( the scene could look like it did in the Omen Trailer).
This makes Noctis go crazy and hatefull, so he allies with Ardyn and absorbs all the starcouge within himself making him inmortal and freeing his enemy from his life.
This way we end up with Noctis in his Versus XIII costume living the Citadel during World at Ruin as Ardyn did, waiting for the next chosen by the Cristal to come. Ending with the first trailer of Versus XIII, where he's attacked by the imperial forces and after that his three bros, Ravus and Cor supported by Lunas ghost come to finish the life of the once ment to be king of light.
Having the option of killing them with Noct or play as them to finish off the protagonist and Ravus sacrificing himself to end Noctis at afterlife.
This way the best posible ending it's still the main one, with the new one having the same results (post apocaliptic world with same survivors) but with Noctis as a villain. Another ending where Noctis destroys the Cristal and everything turns a Dark Souls fucked up world.
And finally justifying Episode Ignis with Ravus being the one who sacrificed to defeated Ardyn and justified Noctis survival.