I do suspect we won't get more than a closing title card that says something like "DW will be back on Christmas Day", possibly with the episode title.
As has been said above, filming on the Xmas special finished months ago - although I'd assume it's probably still in the latter stages of post-production now, adding final effects and musical scoring, possibly even some ADR. (When I was previewing episodes 9 and 10, we were warned these didn't have final visual effects yet. This is fairly common with technically complex shows, with post-production often complete only a few days before transmission.)
It's certainly possible to put together a trailer for Saturday - but that doesn't mean they *will*.
I'm with Batmannequin on this one. I think it's better to allow viewers to absorb and process the finale's ending. Why dilute it by trailing the next story? With regular episodes, it makes sense to tease the next one. With a big, dramatic, season-tying finale and no episode for another seven weeks, there's plenty of time to make it a centrepiece of the BBC's Xmas season trails from early December on.