Quoted from gametrailers.com, "...Namco Bandai revealed the Limited Edition of the game at its recent Level Up event. The LE will include a fully illustrated guide book, an art book, the game's soundtrack, and a collection of "Making Of" movies. Best of all, the LE won't cost you a dime extra than the standard version of the game if you pre-order it ahead of the October release."
You can just go ahead and pre order now, it wont hurt anything. You dont get charged until the game is about to ship, any pre order bonuses are automatically added to your existing pre order. If it turns out there is a CE you would be more interested in, cancel your current order and just pre order the CE. Retailers will not show any other versions of a game or bonuses until the information is relayed to them, even if it gets confirmed via a news outlet.
Amazon just updated it. "Dark Souls Collector's Edition Upgrade: Order Dark Souls and recieve an automatic upgrade to the Collector's Edition for no extra charge. The CE will include a limited edition art book, a mini-strategy guidebook, behind-the-scenes videos, and the game's soundtrack for digital download -- all packaged with the game in a custom-designed metal case. No action is required to receive this upgrade on existing pre-orders."