I'd actually quite like to see Black Rock Shooter and maybe a few other characters from the BRS multiverse make it in. It would be hard to work in BRS's cannon except maybe for finishers, but she does have her straight-edged katana. Strength would be an interesting one with her colossal fists, and Dead Master could be like a combination of Viola and Zasalamel, mainly using the scythe whilst occasionally summoning her skulls for power moves. Black Gold Saw's weapon is basically another one-handed Zweihander, although it's a bit shorter than Soul Edge/Soul Calibur, and you could probably work a bit of variety in there. Chariot has her wheel feet, short sword and massive shield, so she could be an interesting variation on the Alexandra formula, favouring charges, shield bashes and extremely aggressive moves (although obviously you couldn't include her spider tank Mary).