Regardless of anything else, there were so many great aspects of the original Soul Blade/Edge that were jus outright abandoned when Soul Calibur came out. I'd love Namco to revisit some of these;
- Weapon destruction
- Critical Edge attacks (meaningful ones)
- Alternate weapon loadouts to customise each character
- The original Edge Master mode.
And probably a few others I've forgotten.
The weapon loadouts thing has been in up to III at least (and IV, although they made armor effect stats in that one too). V still has it too, although it's only cosmetic and can't be done right before a battle (same with IV).
And Edge Master mode's features have figured into most of the games since then. Soul Calibur had mission mode, Soul Calibur II had weapon master mode, Soul Calibur 3 had mission mode plus conditional stages in Chronicles of the Sword & Tales of Souls, and Soul Calibur IV had the tower of lost souls.