Todd Howard revealed that Fallout 76 will have private servers at post launch, which you can apply mods and change the rules of the game.
Full quote: “When you come into play you can see the other players but you will not be forced to interact with them; you can play on your own. You can see them but you do not have to fight them. Maybe you can use them to exchange items, to join a team, or you can visit their camp. There are a lot of things you can do with other players that is not a comparison with weapons. However, one of our long-term plans is to have servers where you can live your lonely world. You alone. Or at the limit where you can invite only your friends; or you can apply mods and change the rules at your discretion. All of this is in our projects but there will not be at the launch of the game.”