Have they confirmed anyone besides the main character? I don't believe they have.
I wouldn't be surprised if Siegfried and Mitsurugi return. Kilik may as well. But Japanese pop culture is really averse to "old" (i.e. middle-aged) characters. Some of the young girls will probably return too, but middle-aged females are even more of a rarity than middle-aged men.
Ivy will almost certainly learn the secrets of immortality from Cervantes, or Zasalamel, or from Namco Plot Convenience Depot. And she'll be 30 years old forever. I don't think Namco would ever give up youthful Ivy, as her tits are worth their weight in gold.
Anyway, if even half the characters are new, I'll be quite amazed.
Main site is up, but none of the links work yet:
http://www.soulcalibur.com/EDIT: Spoke too soon. Japanese site is up now. The rest will probably follow shortly.
EDIT2: The Guardian (of all places) has art of the new Siegfried. Looks pretty cool.
http://www.guardian.co.uk/technology/2011/may/11/soul-calibur-iv-namco