I keep thinking if The Enemy from "Alien Bodies" had been adapted to series in 2005 by RTD, I would have made them future humans, who are capable of regenerating and altering their DNA, and have become like a fascist totalitarian society. Them in book form could be whatever you want, but if they were to have any impact on the audience or the Doctor it only works if it's someone the audience or the Doctor has a connection with, kind of like an echo of the betrayal felt by what the Toclafane turned out to be, except here they are coming to beat the Timelords at their own game.
