... those posters and photos from The Time Of The Doctor invite some.
Especially the wooden Cyberman.
Is it a creation of the forest like the King and Queen two years ago? Or an actual Cyberman with its armour made of or turned into wood? It appears to still have a metal heart, even if it glows yellow instead of blue. After all, wooden casings for machinery are as viable as metal as long as heat is not an issue.
Helluva way to avert the sonic screwdriver, though...