The Nariko thing would actually be pretty cool....except I dunno about the whole her and Kratos falling in love thing. I like to envision Kratos as being above needing a woman. Same thing for Nariko needing a man.
Anyone who has a problem with seeing women gutted should not be playing GoW, in my humble opinion. The women are always talking about equal rights, right? Well, what's more equal than being gutted in a brutal fashion just like any of the virtual men?
I think it's a fabulous idea! You can't let the whole "someone will complain" limit a possible masterpiece in character design. Besides, make it cool enough and I might play as one myself. Being that athena was in battles and had armor I would think it to be only natural to have a female heroin.