The next game should be "Soul Calibur: Eternally Retold"
400 years after the events of SCV, every character in the series has long since died. However, their souls are not free. When Soul Calibur and Soul Edge were neutralised, they created a 'limbo' where the two opposed each other with equal and opposite forces. As a result of their conflicts involving obtaining, neutralising, challenging these swords, of whatever else they were intending to do, the characters' souls are trapped inside this limbo, never to be freed. Worse yet, no one has memories of themselves dying, so they believe that they're still in the real world, fighting for or against these two swords. Thus they fight fruitlessly against each other throughout the centuries.
This rather dark backstory is, of course, merely an excuse to have the Soul Calibur equivalent of TTT, whereby every single character returns, with the exception of the guest characters for obvious reasons. Thus meaning you can have fun pitting Sophitia against Patroklos, Taki vs Natsu etc.