hmm...i did look over your pic, and notice in your pic to the right of the batter, it looks like a motor would fit right into that gap, it even looks like an indentation was made specifically for a motor there.
and looking at the turret...that indentation where the gear is, looks like a gear similar to the transfer gear on a bit would fit there, and another spur gear would be centered on that tiny hole just to the right of the hole (well, to the right according to the pic, actual position would be a bit back and to the right?) a shaft sits in that top hole and connects to the other hole in the bottom. only problem is trying to transfer power from the motor, which would run lengthwise of the tank, maybe a couple bevel gears could solve that.
but you're right, it does look like a scrapped feature or a future add on.
ahh well, maybe it'll be easier if i could highlight those areas on the tank in your pic (gotta get me photo editing software other than stupid MS paint
)