Just Cause 2 got a huge second wind when the multiplayer mod came out on the PC version about a year ago, which was pretty cool considering the game came out in early 2010. The mod undoubtedly broadened the game's audience and made a lot of fans that perhaps would never have touched the game otherwise, especially when it was nearly four years old. However, Christofer Sundberg, co-founder of the developer Avalanche Studios said that Just Cause 3 will not have multiplayer at launch, saying that while everyone at Avalanche loves the multiplayer mod and the community involved, "at some point you have to make a choice on where your focus is. Our strength is the sandbox experience, and we want to deliver a great Just Cause 3 experience."
As a huge fan of Just Cause 2, I've been trying to keep up with all of the Just Cause 3 news I can, and the more I see of Mr. Sundberg the more I like him. He has been completely honest about the Just Cause games so far, and clearly has a very focused idea of what he wants Just Cause 3 to be, and this all just goes to reinforce that. I appreciate that he is more concerned with making a great game than a game that will possibly appeal to a larger crowd.
He did say that maybe somewhere down the line they will add in multiplayer, but personally I'm not going to count on it. If they can make a great, single player sandbox game, that's more than enough for me.