An image has been posted by DotmToys on the /toy/ board of 4Chan (NSFW) of what could well be the new villain of Transformers Dark of the Moon, Shockwave. As you can see from the image, it’s a very purple Cybertronian looking tank, similar in style to Megatron’s own tank mode in Revenge of the Fallen. Check out the image by clicking on the thumbnail to the left.*
*EDIT: Robot mode image from b-o-t of ACTOYS added!
*EDIT 2: Another vehicle mode image from Yahoo Japan user nihaohuwen added!