Steven Moffat: "They aren't going to make an appearance for a while. We thought it was about time to give them a rest."
Of course, since then he's been on Twitter to say "Daleks: I was talking about THIS series. Stand down."
Got me thinking, though. Daleks might have reached a less-is-more point, where the Inverse Ninja Rule applies so strongly that it would be cooler to see just the one, acting like a villain, rather than a horde of the things invading and overwhelming with numbers. Treat them much like any humanoid villain with a suitably vicious agenda, with minions, room for verbal baiting, and the like.