It's kind of funny, I was wondering if I could predict the antagonist by the mythology they chose for the main character's Persona, but then they decided to move away from mythology and there's no way I could guess.
Hey, if for whatever reason it's NOT a God this time, that'd be pretty cool too. However, this is Atlus, so it's definitely a God.
I can tell you one thing, though: If MC's persona is Arsene Lupin, you're definitely going to see a Sherlock Holmes character and some kind of a Count type character.