I understand how some are calling it a hoax but there is more proof of it being legit.
Reasons why it most likely is legit:
1. Bethesda has only said "No Comment" for the site, when a couple months ago a similar site popped up and they said "We have nothing to do with that site".
2. Eric Todd Dellums randomly tweeting about Fallout constantly for the first time in years (also his whole "are you ready for more 3 dog" debacle at the first of the year).
3. Bethesda just recently liked a Fallout fan made video on youtube. Why would this matter you ask? Because they haven't liked a Fallout video in over 3 years.
4. They decide to start selling new Fallout merchandise 5 years after Fallout 3. Why? (Also the map hidden in the ad and the "more surprises coming").
5. The Site has not been dis-proven yet, although there are negative and positive points for the site being legit. Yet the positive due outweigh the negative.
6. Im on the fence about this one but ill still add it to the list. If Fallout 4 is announced it will most likely arrive in 2014, 3 years after Skyrim. That would follow a basic Bethesda timeline for bringing out games (like I said I don't know if I would really trust this but just sayin).
Feel free to let me know more points for it being Legit or maybe for it being a hoax?
Edit: I forgot to add that all of this stuff is happening within one month. Pretty big coincidence I have to say.