Capaldi Series 8 Costume Hints
They cite a “BBC source” for the info stating:
The decision over the costume was ultimately made by a combination of Capaldi himself, executive producer Brian Minchin, showrunner Steven Moffat and senior members of the art team and had to be approved by senior BBC executives.
Capaldi’s costume mixes old and new – is a “bit old fashioned to denote the fact that he is the oldest Doctor” but is also “looking to the future as well” says the well-placed source.
Interestingly, the site adds that filming has already started on Series 8, but there’s been little evidence of that. Moffat only the other week said it was set for January. But perhaps it is being kept quiet for a reason. Time will tell as always.