Oh, I've just thought of something. Is Capaldi's Twelfth Doctor actually going to turn into the Valeyard?
In A Trial of A Timelord, the Master stated that the Valeyard takes place between his twelfth and final incarnation. Now if Hurt is actually one of the doctors incarnations, that'd make Capaldi the twelfth doctor, but the thirteenth body the doctor has had, so surely this is around the time the Doctor becomes the Valeyard, and it's clear Moffat has not forgotten the Valeyard due to the reference in the Name of the Doctor. And maybe The Eleventh Doctors dealings with the Hurt doctor in the 50th will darken him, so he gradually gets more malicious until finally during some point as Capaldi, he snaps and becomes the Valeyard. Or maybe the doctor is becoming aware of his mortality when he gets to being Capaldi, so he sort of breaks down somewhere in this incarnation and becomes the Valeyard. Maybe Clara will die horribly and this turns him. Plus quite some time ago today, I thought Capaldi would play the Valeyard well, so maybe this is why Moffat has cast him. Maybe it could be what Moffat has planned for Series 8. Heck, the reference in Name of the Doctor could be a little hint like RTD did in his series.