My do's and dont's for 6
1. Keep both swords evil. The Soul Series was one of many parts of my life that showed me that good and evil(in my opinion) are merely points of view, and that good can go too far. And I think challenging this concept can help humanity evolve more and think more critically. So, by having both swords as antagonists, it will make the conflict much more interesting then simple good vs evil. I'd even accept this if Soul Calibur was only revealed to be evil at the very end.
2. Have a campaign that is more than just move from one fight to the next. Say what you want about 5's campaign, but at least that tried to tell a story between it's fights. Have characters evolve, adapt, and do whatever their character requires them to do.
1. Don't give Sophetia a miscarriage. Giving Sophetia a miscarriage would have no other purpose than to satisfy very angry and emotional SC fans, it would not give her development, nor move the story along. I don't care how badly her children were received, a mother suffering a miscarriage is not anything you should celebrate. If the whole thing is a reboot, rewrite Patrokolos and Pyrrha with new personalities.
2. Don't make the conflict black and white. As I've mentioned above, I think keeping both swords evil intensifies the conflict and doesn't baby things for gamers. I was brought into SC via SC4 when the lines between light and dark, good and evil began to gray, and SC, along with other elements in my life including maturing, and reading and watching other stories and games that challenged good vs evil changed my life, and I'd hate to see SC go too far back to a more primitive stage.