How can kratos kill Thor? We all know that fight is probably coming. The whole story will probably loki using kratos to kill the Gods. Loki betray kratos after Thor and Odin is killed. Then kratos goes on revenge against loki for part 5. Typical GoW story.
IMO it woild be a mistake to mess to much with Viking mythology.
In Greece mythology there are no "endtime" myths, only how gods originated... which gave SSM chance to experiment and create their own story.
But Viking myths fully depict how their gods died during Ragnarock. Odin called the help of brave men who were accepted into Vallhala so that could help good gods not to win, but to ensure that endwar would have no victors. Fenrir wolf killed Odin, Thor died while slaying Jormungland (World Serpent from the trailer), fire giant Surtur burned the world, and entire world fell into the sea. After all that madness was done, survivors of humankind emerged in a world without gods.
That's pretty detailed, withnot much space left for Kratos and his tendency to slay gods.
Since he's on the path of redemption, I would like to see him brokering the deal with Odin about calling the help of human warriors.