We called it, after Brotherhood of Steel was confirmed, Bethesda revealed that Enclave will also be featured in the heavily retconned lore of Fallout 76. Considering there will be no human NPCs to interact with, they might just be corpses.
We speculated that the Enclave might be featured in Fallout 76 about two weeks ago, when the news broke that Project Greek Island would be featured as well. The project itself was a bunker that was built under the Greenbrier resort for use by the government, in case of a nuclear attack.
Given that Enclave are the remnants of the US government in Fallout lore, it was an indicator that someone from the Enclave might be there, probably in a state of decay. Bethesda have confirmed that this could indeed be the case, as they posted some background on the Enclave and their involvement in Appalachia on the official Fallout Twitter.
The attached picture features a character in what seems to be an Enclave version of Combat Armour, but considering that the character looks alive and well, it is likely a player or developer who took the screenshot. Fallout 76 might still give us some passive storytelling though, via holotapes, notes and terminal entries.
Since Bethesda explicitly stated there will be no human NPCs to interact with, Brotherhood of Steel and Enclave involvement will likely be limited to holotape-driven quests that will serve as a source of power armour sets. It is not entirely clear whether launch code drops are randomly generated on random ghouls yet, but intuition would dictate one of these factions managed to get codes beforehand and would therefore have them for players to loot.
On the other hand, the "secret bunker deep in Appalachia" that Bethesda mentioned could be a place where players will be able to launch the nukes from in the end. They didn't confirm nor deny whether this bunker is indeed Project Greek Island though, but considering the ties to the government, it is heavily implied.