The director of Just Cause 2 is loud and proud about the fact they built a single-player game, and shut down thoughts that they could be cooking up multiplayer downloadable content for this game.
Still, Magnus Nedfors told Eurogamer that his studio, Avalanche, has had "lots of good ideas" for a multiplayer Just Cause, but it would likely be realised in a completely different future version, not as an add-on to this one.
"There is no current plan for DLC allowing co-op gameplay," he said in a reader Q&A. "I'm sorry. We opted from the beginning to make a single-player game. Adding multiplayer would have meant limits on what we could achieve. I personally – not the company – think single-player games are great fun and there is an audience for that. A game can be good without multiplayer support."
That doesn't mean there will be no DLC support for Just Cause 2. We just don't know what it will be yet. Other than not multiplayer, that is.
Just Cause 2 [Eurogamer]