The rumors are true,
Nuka World will be the next FO4 dlc. It looks like it will allow you to become a Raider.
There is also a Vault Tec dlc that apparently allows you to become a vault overseer and even perform experiments on your vault dwellers. It looks like the final dlc is one called Contraptions, that apparently allows you to build more stuff like conveyer belts.
Here is a vid with Bethesda's E3 announcements