Here's the screenshot of it when it was on the Xbox Marketplace:
*MARKETPLACE IMAGE*
What this leaked:
Location is Ventura Bay
Extensive visual and Performance customization (yay)
Five ways to play: speed, style, build, crew and outlaw.
Multiple stories that can overlap each other
Reputation that you can gain as you progress through the game
In the Porsche screenshot there is a license plate that says "ANAKAI" so I'm guessing that it's the return of bosses or there will be customizable license plates (or both)