I think the problem is, there one of the best dr who baddies, better than the cyber men etc imho, and also had the ability to travel in time, and seem to have the ability to lay dormant etc for 1000's of years.
So they could be seeded all over the place, i'm sure its no coincidence they keep them alive time and time again with the glimour of hope i have no idea how they reproduce... or if they're grow so dont know how 2 somewhere could become many etc.
Will be another interesting story arc as they always are with the daleks involved. After all some of the baddies are down right pants! Those robots in masks, the dalkeks pig goons.
But its not a serious sifi, its spoof tastic it always has been, even the daleks could be foiled by throwing your coat under them and shoving them down a lift shaft. Of course they seem to be one of the few to recognise the doctor and fear and revere him, his nemesis throughout time.