Ok, heres a picture of that guy with the cracked helmet.
SPOILER!!! (if you wanna wait to see him in the game then dont click the link!)
Yes..looks like Sora neh? perhaps him in the future, maybe his son or perhaps it's Roxas..not certon though.
The creator did say the three characters at the start are not Sora, Riku, or Kairi..but he didn't say that they wouldn't appear in it completely.
Also, Kairi was not created by Ansem...actually the very though of that just scares me...very much...I will have nightmares from now on. Ahem! Anyhow, She was born in Hallow Bastion, you see her younger self in a clip when Sora first enters the library in KH1. Hallow Bastion used to be known as Radiant Garden, which was a prosperous town before Xemnas came into existance.
I also believe KH3 might revolve around Roxas and Namine, but it's just my guessing. I look forward to more spoilers.