There are probably two demographics (speaking generally)
Those who are aware of Fallout 4 and those who are not.
The aware
It would be hard for those who following gaming media and the forums to miss the arrival of Fallout 4.
The reveal trailer on youtube has been watched 16 million times and that excludes mirror copies.
The game press/media are falling over themselves to make even non-news discussion worthy.
So if you know it's coming, you have seen a trailer and representative gameplay from the E3 showcase.
That's enough information to allow a purchase to be provisionally made (pre-reviews).
More trailers won't sway someone more.
The unaware
We're 49 days from launch (7 weeks), the time for game posters or other trailers (they could use the same one)
to be out there for the unaware is just before and at the point of launch (also for holiday shopping) it's not now.
Skyrim's live trailer was 2 weeks before launch, not 7 weeks before.