I'll address a few points raised on the status.
What could it be? Probably a sequel/sidequel set in a different area. And I echo your thoughts on it being an MMO.
Hey, check this out! Right-click the countdown and select "View Page Source." About half-way down the code, you'll discover the following:
PA system failure has occurred.
Shutdown of the Masterbrain has been authorized and all sensitive materials have been removed for security purposes.
Please attempt re-access. Have a pleasant day.
Click for a larger image. I circled the text.
Masterbrain or Institute?
Masterbrain is a robotic brain that controls the security robots in the corporate headquarters. Maybe it was hacked?
I think Institute was the code name for Fallout 4, but I could be wrong, and it's also an in-game facility.
EDIT: The Blood Steel dlc talked about it. I don't remember much but someone was supposedly going to the Institute.
It means we probably know where the game will be set: The Commonwealth
Do you remember Masterbrain?
I can clearly imagine a trailer with this song. It has to be in the game.