The very first trailer of Fallout 4 was released and all the previous speculation was confirmed. Fallout 4 will take place in Boston, more precisely around Vault 111.
There is not much information available as of now, I guess we will have to wait till the E3 of this year, just about 2 weeks from now. It’s kinda strange that the developers of the game have released several images of their development kit and some pieces of information about this game, but the head staff of Bethesda always rejected and denied any speculation surrounding the in-development state of Fallout 4. The bigger video game outlets on YouTube and big gaming websites concluded that Fallout 4 was likely not in development until they saw the countdown on the official page of Fallout 4.
The in-game trailer features power armors of the Brotherhood, a new possible companion (a dog), new locations: Boston and its surroundings and some collectables, like magazines, and random stuff which can be collected by playing the game.
Looking at this trailer Fallout 4 look like a lot more colorful, than Fallout 3 or Fallout New Vegas, and the story may include areal vehicles, such as the Vertibird.
Fallout 4 will be likely to be pushed out to PC, Playstation 4 and Xbox One, although this ifnormation is yet to be officially confirmed by the developer team.
Looking forward to the E3 2015 show of Fallout 4. I guess The Elder Scrolls VI (: Redguard?) is already in development.