Kratos defeated the Greek Gods
And there have been many speculations which Gods will be next.
Many have talked about The Norse Gods
Some about The Hindu Gods
And also the Egyptian Gods.
you can also see in this link an article
Talking about options for Kratos Future Plot.
Check out this link -
http://moviepilot.com/posts/2015/06/10/god-of-war-4-are-these-the-gods-kratos-is-tackling-next-3296822?lt_source=external,manual
And tell me what you think.