Not yet, but they will be.
According to an interview with Nerd3, showrunner Steven Moffat says that The Doctor's choice of face is something that will be addressed in-universe.
I remember Russell [T Davies] told me that he had a big old plan as to why there were two Peter Capaldi’s in the Who universe: one in Pompeii and one in Torchwood. When I cast Peter and Russell got in touch to say how pleased he was, I said, ‘Okay, what was your theory and does it still work?” and he said, ‘Yes it does. Here it is…’
We’ll play that one out over time. It’s actually quite neat.
There has already been a sideways reference in "Deep Breath" as The Doctor thinks aloud:
DOCTOR: ... Er, have you seen this face before?
DOCTOR: Are you sure?
BARNEY: Sir, I have never seen that face.
DOCTOR: It's funny, because I'm sure that I have. You know, I never know where the faces come from. They just pop up. Zap. Faces like this one.
DOCTOR: Why this one? Why did I choose this face? It's like I'm trying to tell myself something. Like I'm trying to make a point. But what is so important that I can't just tell myself what I'm thinking?