It's not a surprise that the Cybermen would be returning for Eleven's final adventure, in fact it's pretty much required. What is a surprise though is the fact that we've learned that there's a wooden variant to the traditionally metal menace. Now besides the obvious reason of confounding The Doctor's screwdriver, seeing as it didn't used to have a Wood setting. However, that reasoning goes out the window now that The Day of The Doctor solved the dilemma by using a little bit of timey wimey logic involving The War Doctor. So the question still remains: why would a species bent on technological superiority build their own demented version of Pinocchio? My guess: either they didn't get the memo and think this is a proper Doctor-proofing strategy, or they want to use it as camouflage amongst Trenzalore's forests.