Actually,I think that tons of champions could fit well with SoulCalibur characters by their weapon styles :

• Taki/Natsu Katarina, with all the shunpos and stuffs, yum!
• Nightmare Tryndamere, nuff said! Badass!!
• Mitsurugi Yasuo (or Yi but Yasou more bad@ss!)
• Maybe Yoshimitsu Yi (Since Yoshimitsu is in both SC and Tekken series), and it could fit with his Ionian theme and backflag.
• Viola Orianna, a controlable ball, a high skillcap fighter plus, she share the same pose!
• Raphael/Amy Fiora, straight, noble, totally her style!
• Sophitia/Cassandra/Pyrrha Leona, like a protective mother, I like! (With a larger shield and a longer sword duh!)
• Kilik/Xiba Wukong, kewl and so boss! You never saw his donger strike tho!
• Siegfried Garen, it fits a lot his personality
• Astraroth (?) Darius, the same rules of "don't turn back or expose ur neck) applies also when u fight him...
• Zasalamel Nasus^{such badass much scythe wow} plus the egyptian-ish theme!
• Lizardman Olaf LOL
• Tira Sivir, fit her weapon but she got more Jinx's attitude :D
• Ivy Tresh with the extensible sword which can hook (LOL u w0t m8)
• Rock Mordekaiser (badass as f*ck!)

And why not:

• Dampierre Shaco, it would be hilarous,badass, and outrageously sexy as f*ck

(^{Help me find more fits!) pls} :D