Hey, so I have a crackpot theory I'd like to share.
In the first Dissidia, the characters were all drawn by Nomura with influences of Amano on each, right? In a way, their 'Nomura-look' was their main costume. Since Duodecim is a prequel of sorts, maybe the developers are reverting some of the characters back to their Amano art, this time with Nomura influences as a way of communicating this link with a previous cycle. Just like Amano worked before Nomura, so too are the characters taking up primarily Amano designs to fit that.
Essentially, all the images we've seen of characters in their Amano art isn't their alternates, but rather their new mains. Make sense? I realize that Nomura is still doing the designs, but maybe it's the look he's trying for.
Also, I'm excited for the new story mode, mainly because I want to see heroes die. Not cheeky 'gameplay death', but actually dying so their only chance is a revival in the next cycle. I think this game's equivalent of Shade Impulse should feature the heroes getting picked off, each getting their own final battle, until only WoL or something tries to fight Chaos. It'd force you to use someone you may suck as, but would be very interesting IMO.