I honestly don't think that there will be multiplayer for Fallout 4. If there will be it will be like Skyrim online, it'll take them three years before it gets released. But if they did release online multiplayer for Fallout 4 in the future, then that'd be dope AF.
I may be wrong but I honestly don't see them launching multiplayer for Fallout 4, the games have always been heavily focused around you being a lone survivor so it might take that factor away. On the other hand that may have been due to the old generation systems not having the power to do so though, who knows what we'll see!