Chris Avellone on twitter hasnt been saying much, but reading a few of his tweets it sounds like Fallout 4 isnt too far away from being finished.
Specifically a tweet in reply to asking if Fallout 4 would be out my 2015.
He said "Thats up to Beth." instead of an "I dont know" or "I cant comment" leading me to believe that it's pretty close to being done and they arent sure when to release it.