With all of the enhancements that Far Cry 5 will be making, namely to its exploration, it sounds like co-op will still have its limits. As reported by RealGear, Far Cry 5's co-op multiplayer mode will only award mission progress to Player 1, forcing Player 2 to have to replay the game in their own time. The co-op mode is online only (of course) and is designed with the ease of drop-in and drop-out in mind.
It's unfortunate since this limitation was prevalent in Far Cry 4 as well, and it seems that the mode took a bit of a backseat in terms of importance to evolve. That said, it's possible that the developers felt that the mode wasn't used enough to warrant major development time to, but then again, having only one player progress takes quite a bit of wind out of the sails.
Far Cry 5 releases on PC, PS4, and Xbox One next year on February 27th, 2018.
Source: [RealGear]
