Timed exclusivity is still ‘exclusivity’ at the end of the day.
Batman Arkham Knight is one of the very few third party games that has a form of timed exclusivity deal with Sony. Now, this doesn’t mean that Rocksteady are releasing the game exclusively on the PlayStation 4, rather that the game is getting timed exclusive content.
This content, that is exclusive to the PS4 for the time being, comes in the form of Scarecrow Nightmare missions which are bonus content missions that see you tackling the Scarecrow on his terms. There are other pieces of exclusives that come in the form of custom skins for both Batman and the Batmobile. They are the Classic TV Series Batman skin, in the vain of Adam West’s somewhat camp Batman that remains a cult hit, and the Justice League 3000 Batman, a ridiculous looking red and black armoured suit. The Batmobile skin is the Classic TV Batmobile and it too sports a red and black design, though it is decidedly more appealing than the JL 3000 Batman suit.
The extra content is said to be exclusive “until at least fall 2015” at which point it will presumably make the jump to Xbox One and PC builds of the game.