This is an interesting idea... I kept thinking that they're going to move forward with the series but going back actually makes more sense because now they still have access to all the gods and the world hasn't ended.
But part of me wonders why they would go back... granted, after GoW3, it would be hard to go forward. So maybe this is some kind of time thingy where this omnipotent being (you know there's one, or why else would Athena exist) asks Kratos to go back in time and fix things. But Kratos is all like, "Aw Hades naw!" but then this omnipotent being says, "but you can save your daughter/wife/mother/brother". And...
*Kratos puts on sunglasses*
YEAAAAAAAAAAAAAAAAAAHHHH!!!