Man man man I can't believe what I read!! I hope I wasn't the only one who didn't know it!
I knew Sephiroth appears in AC, but I though he does it as a flashback(although in one of the trailers he seems to be in a non-flashback scene) So, looking for the article Zerosmus recommended us I saw a summary of the plot of AC in which it says that someone 'who should be dead' appears again. It seems it confirms that the warrior with the long sword comes again? XDDD
I think there might be more than one summon in the movie!! Bahamut's ok, but why having idle summon warriors?
I'd like to see Odin for sure in the movie, wouldn't you like? Thank's for the link Zerosmus. If you get something more, let me know
PS: BOY, THIS LINK IS AMAZING!!
By the way, is Nobuo Uematsu composing the music again? I hope so.