At the Cheltenham Literature Festival in early October, Moffat told the Radio Times:
"It's too early to put it on. If it were up to me, the BBC would only publicise Doctor Who and Sherlock. However, in their biased and wrong-headed view, they have a number of shows on before Sherlock and Doctor Who that they have to publicise now, so they’re waiting to publicise Doctor Who and Sherlock until later.
“I agree it is a crime! Who cares about those other shows? I don’t! But I have to wait in line, so the reason you haven’t see the 50th trailer yet is it’s too early to put it on. But it’s not going to be very much longer…”The official Doctor Who Tumblr also confirmed in a reply to another user that a trailer for The Day of the Doctor will be coming soon. Trailers typically land 2-3 weeks before a broadcast, so expect the trailer in early November...
[Source: Doctor Who TV/Radio Times]