The Steam pre-purchase page for Resident Evil: Revelations has been updated with a bevy of rewards for pre-ordering the game, but the most notable is Reward 3, which offers to “Fight the fear with more weapons and more characters! Expand your RAID mode experience Resident Evil Revelations Season Pass which includes 4 pieces of additional content. ” Directly below, it says that the content will “be revealed and available shortly after the game’s release.” It’s likely that this will end up being more maps for RAID mode and nothing that directly impacts the single player story. It’s been said before that the console versions of the game will have DLC released for them, so it’s likely this will surface there as well.
Of course, this offer will only be unlocked on Steam if a certain amount of people pre-purchase the game. Other rewards include an artbook and soundtrack and Lost Planet: Extreme Condition for some reason.