The mod team that brought you the fantastic Just Cause 2 multiplayer mod is at it again, and by that I mean it's developing a multiplayer mod for the more recent Just Cause 3. You can see the early stages of progress in the video below. There certainly seems to be a long way to go, but it's proof of progress if nothing else. Don't mind the poor draw distance, which seems to have been turned down for demo purposes.
There's word that the Denuvo DRM included with the game is causing development issues, so you can expect a longer development cycle than normal. There's also the chance it proves so crippling that the project doesn't reach the finish line, although the team is said to be tight with the Just Cause 3 studio, making that less likely.