If you haven't already played the God of War Collection, feel free to read my review here. If you have already played the Collection, then you probably have an idea to what I'm saying here. It is possible that the next God of War may include Kratos' brother in some way, and here's why.
One of the trophies in God of War 1 (in the Collection) is called, 'Legend of the Twins.' This is a silver trophy and all it requires you to do is watch the 'Birth of the Beast' treasure that you unlock after finishing the game on any difficulty. You can watch the video here if you missed out.
The video explains that Kratos and his brother grew up in Sparta, in which the weaker children were sent to die in the mountains. Kratos escaped this fate, but his brother didn't, and now he wants revenge on the brother that abandoned him.
Of course, this video has been available since God of War 1 released on the PS2, but was merely considered as a back story. However, the fact that the developers value this as a silver trophy suggests that Kratos' brother may be one of the enemies in God of War 3. I mean, why else would the reward you so much to watch a video?
There is however, still the concern of, 'how does this fit into the story of God of War.' Well, whilst God of War 3 is the end of this story, John Hight revealed in an exclusive interview with HipHopGamer (~39 mins in), that it isn't the end of the God of War series. So it is even possible that the next story in God of War will be based on Kratos' brother, we may even be playing as Kratos' brother, who knows?
In any case, it's a great time to be a God of War fan, and we're looking forward to March.