OBL dead doesn't mean the "War" on terror is over.
BlackOp sold pretty well so I don't see Activition/Infinity Ward is going to stop making more COD.
I agree, 'terrorists' are going to be the villain of choice for awhile yet. There is just a large market for 'realistic' FPS games, where realistic is defined as fighting with modern weapons against an enemy that the US might actually target.
I saw a recent Cracked article that said all the classic villains are dead. We need to find something genuinely new and it doesnt look like the industry is into "new" these days.
New is dangerous. Put out another CoD and you are pretty much guaranteed to make money, make a game that is new and different and you might create a new franchise that will last 10 years, or you might lose your shirt.
Personally, I would like to see more futuristic enemies and weapons. Let me fight aliens, or zombies, or monsters. Give me an arsenal of 30 weapons to fight with, and limit my choice of which ones to carry to just a handful. Let me choose if I want a 38 pistol or a pulse laser, a flame thrower or an assault rifle, a rail gun or landmines.
Borderlands did a decent job of this, and I think it paid off. Now others need to find a way to adapt this to other types of FPS games.