Well, so far, all of the spoilers I've heard about the Christmas special have turned out to be completely true. Now there's a shocker.
Also, filming on Series 8 has begun.... indoors. But with location filming just around the corner, I wouldn't be at all surprised if we find out what Capaldi's costume looks like within the next couple of week's. According to this article, it's going to be "a bit old fashioned but also looks to the future" which you could say about pretty much any of the Doctor's outfits, with the possible exception of Eccleston's.
Since Capaldi's favorite Doctor is Hartnell, and he's keen to play an older version of the character, I wouldn't be surprised to see them go for something in a dark-colored frock and scarf, similar to what Hartnell wore in An Unearthly Child. Or I suppose they could alway go for something like this wonderful photoshop job from Gallifrey Base: