I don't know if any of this was mentioned but these are my thoughts.

Innocence isnt a sin eater like the others. I feel that they, since we don't know if they are male or female, are "human" in some form. I have two thoughts on that. Either they are someone who will become Innocence, someone new or old. Or I feel that they are a part of Minfilia. There has to be a reason why she's regressed to a child. Maybe it's because her Innocence was ripped from her.

The other thing is about the level 80 job quests. Basically, the normal flow of the game has you wanting/needing to do the final job quest before headed into the final dungeon or trial. Well while we dont know how our adventures on the 1st, speculation would have us think we'd be staying there until things are resolved. If that's the case, we'd be headed back to the source to do our job quest and other sourcey things. The fact that the sixth zone hasn't been revealed yet hints at this as well.