Alright, so I have come across a few things that may suggest fallout 4 being announced on the 11th of December, 2013. What I have come across is a blog (http://12072299.tumblr.com/), and it contains audio files that were cut content from fallout new vegas. It contains a Vault 74A audio log that was planned to be put into fallout 3, then taken away, then added to New Vegas, then also being taken away. I have read on other forums that the blog has been registered by Zenimax Media, the owners of Bethesda. There is also a countdown, and it can be linked here (http://www.thesurvivor2299.com/). You cann find vault 74 info here, but there is http://www.thesurvivor2299.com/ speculation from these websites that suggests that the new protagonist might be called The Survivor, like how in Fallout 3 you are playing as The Lone Wanderer or in Fallout New Vegas you are playing as Courier 6. Keep in mind that in the background of the survivor 2299 website you can hear what might be binary code, and I have no idea what this translates to. But in the audio log in the blog site that I linked, it mentions that they were invaded by fiends, leading to the title The Survivor, since you are the only one to survive the fiend invasion. You might even be the overseer, because in the page on the wiki for vault 74, it states that the vault itself in the game was very small, with only an atrium, a vault door area, and an overseer's office. Not much else is known about what happens from here on out, but be invested.
http://12072299.tumblr.com/ for the audio files
http://www.thesurvivor2299.com/ for the countdown and the binary code
http://fallout.wikia.com/wiki/Vault_74 for more info on vault 74