I agree that the Daleks (and possibly the Cybermen) could do with a rest. Maybe they could bring back some of the older villains such as the Sea Devils (maybe a chance of a Lovecraftian homage there), or the Ice Warriors.
What about an ad-hoc poll as to which adversary we would like to make a comeback?
Well, I would have said the Silurians, but they came back in one of the better stories last series. I say...the Ice Warriors, the Great Intelligence (along with the Yeti), the Draconians (who are mentioned, but not seen in The Pandorica Opens
, though the new Silurians look a bit too much like them), the Weed Creatures...hell, I could name a dozen or more Doctor Who
monsters who deserve a comeback, never mind one-shot villains like the Celestial Toymaker, Omega (who is rumoured to be the ultimate villain of this series) and Fenric.
I've lived for over 2000 years, and not all of them were good ones. I've made many mistakes. And it's about time I did something about that.
-The Twelfth Doctor, Doctor Who: Deep Breath