So I'm really into Undertale, and the fandom has created a BUNCH of AUs for the game. My favorite is called Storyshift. Basically, the characters maintained most of their personalities, but their place in the story changed (ie one character who was queen in canon is the captain of the royal guard in Storyshift). It'd be cool to see something like that for FFXV.

In the hopes of encouraging multiple fills here are some ideas:
Prompto is the prince, not Noctis (and Noctis is the MT from Nifleheim)
Gladio and Iris switch places with Luna and Ravus
Noctis takes Ardyn's place and Ardyn is the chosen king

Stuff like that! I have no pairing preferences, and if you want to include smut I don't mind at all, but I'm more looking for story differences here. Have fun! (I would be happy with short or lengthy fills!)