Remember the sisterhood of Karn? They appeared in The Brain of Morbious along with Tom Baker. They where good friends of the Time Lords and claimed immortality via the flame of life. They also had power over how time lords regenerated. They appeared again in 2013s Night of the Doctor to make the 8th Doctor regenerate but only this time he could chose the outcome because time lord science is elevated on Karn. My last remark on this part is that they all where ruled by a leader.
Now, cast your mind back to The Fires of Pompeii which featured both Peter Capaldi and a mysterious sisterhood who share some unbelievable qualities with the sisterhood of Karn. The first being the obvious dress sense, red capes and cloaks etc. the envy being that they too where involved with fire and where ruled by an mysterious authority figure. They also had physic powers for a short period of time.
I believe that the sisterhood of Karn is behind 12s appearance. Do you?