Fallout games have featured many landmarks and secrets throughout their history and it appears Fallout 76 will be no exception. Bethesda has recently revealed that the Greenbrier landmark will feature the secret government bunker.
Project Greek Island will be featured in Fallout 76, as a part of the previously shown Greenbrier Resort, which also serves as one of the West Virginian, or Appalachian if you will, landmarks. The news broke out as Larry "Major Nelson" Hyrb who attended a preview session of Fallout 76, at Greenbrier itself.
Considering that Bethesda-era Fallout games always featured landmarks and secrets tied to them, the inclusion of Projekt Greek Island is not that much of a surprise, but a point of interest nonetheless.
For those unacquainted with the source material, Projekt Greek Island is a bunker built as a part of government continuation program in 1958, due to the concerns of a nuclear war. It would house members of the Congress, where they could live and transmit broadcasts thanks to an emitter build nearby. The bunker was a strictly kept secret until 1992, when it was exposed by The Washington Post.
Now, when you mention "government continuation" in the context of Fallout, one can't think of anything other than the Enclave. This opens up many opportunities for Fallout 76, but Bethesda previously stated that there will not be any NPCs to interact with in the game, so it's unlikely we will get to see or fight an early version of the Enclave.
Still, in the alternate history of the Fallout universe, the government could have kept using the bunker as it maybe never got exposed. Even if we don't cross paths with the Enclave in the flesh, it would be a nice touch if Project Greek Island ended up being some sort of their stockpile where players could eventually find valuable loot. One can dream, right?
It's also a widely known fact by now that Fallout 76 will feature nuclear bombs that players will be able to use on their opponents, so Project Greek Island might have practical uses and not just be a loot room. It could pay off to build your settlement close to the Greenbrier, we will see.