Part of me hopes this is just an incredibly elaborate hoax, just to see everyone's reaction, but the more this stuff continues the more convinced I become. I think this Fallout 4 thing is legit.
The above screenshot comes from the latest discovery. A complete new website within the original website. I have no idea what this all means because I'm not invested in the Fallout universe like that, but this incredible Google Doc has all the information you need and also updates to include all the latest info.
If you are excited about the possibility of a new Fallout game, that's the site you want to be keeping an eye on.