I wouldn't mind seeing Nariko, but i'm not clamoring for her either. They really should have followed up with another game. Oh and i played both Heavenly Sword and GOW and while they are very different i also found they feel a little similar, especially with her range.
They probably could have handed the IP off to a 2nd party to develop and I think Ninja Theory did have some stuff ready for a sequel but they decided to pursue the multiplatform pastures to get better sales...which didn't turn out too well for them, especially after Namco had made the comment about wanting the Enslaved IP (specifically 2 & 3 whenever they came along) to be their Uncharted/Gran Turismo 5 and the future for the company...
Sony should probably regulate some of their unused IPs (Heavenly Sword, Colony Wars, Omega Boost, Legend of Dragoon, Kinetica, Rogue Galaxy, etc.) to the Vita to give them some new life and to give the Vita it's own library of solid IPs/exclusives on top of the PSP titles/IPs that will most likely migrate there (Syphon Filter, Patapon, Loco Roco, etc.).
I like Asbel Lhant from tales of graces. Newer rpg but ive always liked the Tales series. With 2 battles stances and plenty of artes to choose from i think he would be EPIC
As much as I've been against his inclusion, I actually think Dart from Legend Of The Dragoon would be a prime candidate for a pure swordsman character (since all the dragoons could only use magic in their dragoon form).
I think there's a ton of other characters who can provide that and more though, so it just depends on whether you want a close-up fighter (like Heihachi with a sword) or someone a bit more varied who also uses a sword. I can imagine Wander and Samanosuke filling that role because they both have ranged weapons or Cloud and Monica (Dark Chronicle) filling that role because they use magic. Sir Dan, however, could be the most versatile character on the roster if he's included. It's actually his range of weapons that make him not the best candidate to be a swordsman because every weapon in his arsenal is so interesting! Yeah, he has three swords but also an axe, a club, a hammer for close-range combat, a crossbow, spears and three longbows for long-range combat and lightning, chicken drumsticks and his own arm for ... erm, "weird combat". And that's just the first game, before we bring on the bombs, gatling gun and blunderbuss ...