I am a fan of God of War...and that's why I think Kratos needs to end. Kratos was a war-obsessed Spartan who desire to win at battle at any cost, led to him killing his family. He was a tortured soul looking for peace from the Gods, but coming up empty. His revenge is predicated on that. Kratos has exacted his revenge. He's killed any and all Greek Gods of note. You can find obscure creatures in Greek mythology, sure. You can make up your own creatures, sure. That's what Ascension did...and its one of the reasons why Ascension didn't strike an accord like previous entries. Kratos' arc is done. Sure I thought they could have humanized his character more (something they kind of lost sight of in installments after GoW1), but changing mythologies, or finding some new villain is a bad idea in my mind. Its the equivalent of Hollywood execs dragging a tv series for an extra season or 2 because its popular. You lose the integrity of narrative. You lose the integrity of the character. Kratos was designed for Greek mythology. His motivations were designed for Greek mythology. It doesn't make sense for him to be trouncing around in Egypt or Norse mythology.
Reboot/remake the series. Do the Egyptian/Norse mythology, but with a new 'rage' character. Take Heaven Sword, let SSM give it the God of War treatment (in place of Ninja Theory's efforts), but let Kratos rest. He's had over half a dozen games. The writings on the wall, the media isn't going to be kind to another Kratos GoW.
I think the Heavenly Sword IP would be good because, you keep the chained blades and sword. It allows them to have a drastic change in scenery and mythos. You get all new characters, and you aren't limited to what's found in Greek mythology; you can create as many new enemies, villains, as you want. It allows them to change up the fighting style from more of a barbaric style to one of martial arts. It allows for new platforming and puzzle mechanics. That's enough new features that it will feel fresh. With a new IP, expectations will change, even though they can have a lot of the same base mechanics.