In an interesting twist of marketing, not only will Deathstroke be a key villain in Batman: Arkham Origins .. you will have the opportunity to experience the game from behind his mask via pre-order DLC.
Remember playing as Catwoman in Batman: Arkham City? It looks like this trend will continue on with Batman: Arkham Origins, but with what should be, an even darker twist. Catwoman was always in the ethical shadows, playing both good and bad sides to her favour. Deathstroke, not so much. He's very much the darker anti-hero at best - which is saying something in a Batman game. Combine that with the fact that Deathstroke will be a key antagonist, things might get rather interesting with how they package his player-controlled role. It should also be noted, that Ron Perlman will reprise his voice acting role within the game.
How "exclusive" this DLC will be, has yet to be seen. If the past is any measure, these types of DLC tend to filter their way down to those who wish it via the store on your preferred platform. The key, as always, will be whether or not you wish to wait and see if this occurs, or to get in on the action from day one.
You have till the 25th of October to decide which way you'll go. Personally, it will be a pre-order for me.