Heihachi will be playable still
[Update: Online multiplayer has been confirmed, and the online infrastructure will feature brand new netcode overseen by the Project Soul development team.]
Namco Bandai revealed Soulcalibur 2 HD Online at their San Diego Comic-Con panel today. It'll be out this fall for the PlayStation 3 and Xbox 360, and guest character Heihachi will still be featured at the very least. You can expect all of the original modes to return as well, plus the obvious inclusion of online multiplayer.
No word if Spawn will still be in the game, and we can pretty much count out Zelda's Link considering there was no Wii U version announced.
That's all we know for now, but will update you once Namco releases more info.