I'm assuming the dungeon is some kind of way to the 13th and were going to fight golbez in the moon also they can put a 2nd or 3rd phase to implement zeromus or fuse with zero and the dragon and golbez in some way to make zeromus or zeromus himself will appear after kicking golbez ass if they somehow try to go with ff4 script but I'm certain he will show up in the next patches or even expansion or could do 2 world's in 7.0 where you go to myracydia or somewhere in eytheris and go back and forth in the 13th or void like they did with shb. But who knows knowing them they will do some kind of main entry merge to have some nostalgia.