Everyone here says that (well not everyone, but many people) but that doesn't account for the millions that buy the games. This is probably a vocal minority and as such I imagine that it will be Kratos in the next game.
Personally I'd prefer him but wouldn't be too bothered should it be a new character or some type of reincarnation. Would seem a bit silly to remove the iconic character for the PS4 game, especially seeing as many PS4 owners may have only changed consoles this generation. I thought that was also the thinking behind the release of GOW3, to whet the appetite for this.
Story wise, it'd make tons of sense to replace him. For one, His story was well done imo with 2. And I actually liked him up until then. Plus with a new mythology, his fanfiction gary stu nature steps itself up a notch in abrasiveness. And more than anything, Kratos would be fantastic as a villain. All great story reasons to not make him the hero.
As for marketing reasons, as the villain, they could still put him on the box and all over the trailers. Plus notable other series have attempted a main character switch without going up in flames.(suprisingly enough as first entries on a new console as well), DMC Metal Gear for instance. And their mains weren't reviled like Kratos is. The switches also didn't take, but that didn't stop mgs2 from being the best selling mgs ever.
Point is, it's certainly not suicide to switch him out.