In the title screen panorama there is a tardis with a weeping angel inside. I figured that was an easter egg, but I belive it could turn into a good boss from both a gamplay  aspect and a story aspect. In the 10th episode of the 3rd season of new who, the doctor says: "The blue box, it's my time machine. There is a world of time energy in there they could feast on forever, but the damage they could do could switch off the sun." .

I belive there coul be a weeping angel boss in the ruined citadel of the Time lords. An angel found its way to gallifrey and feasted on all of the tardises that remained after the war. The boss could be defeated by overflowing the boss with time energy, or with another weapeon found in the citadel.