I'm inclined to think that these AT-ATs will be more involved than what meets the eye. While clearly the legs are stationary, the head could actually be remarkably complex. An AT-AT head has four weapons mounted to it. Two under the cockpit and two on either side of the pilot. AT-AT's weapons are extremely powerful, and as a result recoil. That quick pulse after each firing is a quintisential part of their look and feel. Additionally the side mounted weapons are equipped with a greater freedom of movement, being built onto a rotating joint that moves vertically to the ground. This gives AT-ATs greater flexibility for both close range ground targets and aerial targets. These particular features (recoil and rotating joint) can be seen clearly in this quick compilation of AT-ATs from Hoth: I suspect in Disney's obsessive focus to detail, these characteristics won't go unnoticed. I'm guessing many Star Wars nerds who know Episode 5 by heart are working on this! So considering the idea these heads will be supporting 4 constantly recoiling and possibly pivoting canons with electrical for lights and simulated lasers the overbuilt head becomes more reasonable. Now obviously this is conjecture, but with this attraction I'm betting on more realism. Static AT-ATs wouldn't fit the bill.