I really like the trailer.
The first time I watched it, I thought it was hilarious--a great mixing of elements from the show with an acknowledgment of fandom. But I was a little confused about the woman with the nose ring, wondering who she was. And I didn't recognize Anderson for who he was!
Then I watched it a few more times, after reading the comments here, and a had a few more reactions: I agree that it's Sherlock at the gravesite; I think the flowers are more likely from his fans (of which we know from Series 2 there are many); I really don't like John with a mustache!; I have no idea what Anderson and the others were doing in that apartment/flat and don't want to speculate as many others here have already come up with lots of possibilities; I wondered why Anderson doesn't have a cell phone of his own--he has to look at someone else's to see the message--why?; I loved all the text messages appearing on screen--a clear link back to Pink so reminding us of the continuity of the series, even though the directors are not the same for Series 3; but the multitude of texts also kind of reminded me of the end of Hounds, when we see Moriarty in the cell and he's scribbled Sherlock all over the walls.
But what I really want to know is: When two people are opening doors for Sherlock, after the shot of John--where is Sherlock going??? It looks like he is walking into a business establishment--could it be the restaurant where John was in the first trailer? I love how Sherlock strides confidently through the doors; it's as if they are the kind that automatically open when a person nears them, instead of being manually opened by two people. Is this the scene when John finds out Sherlock is still alive?
I know that "trailer" and "teaser" are used interchangeably but I think this video is much more a true teaser than a trailer, in that it is playing with the audience and clearly was designed to provoke comment about it. So ti has worked brilliantly!
As for not announcing a date, perhaps the BBC still hasn't figured that out. I read somewhere that such decisions are made very close to air date so maybe they really haven't decided yet when to broadcast the show.