Yeah, true, Welker having a VA role in the film is most likely just a rumor. However, I had a concept as to who he may voice. Soundwave. Come on now, stay with me here... What I'm envisioning here is an after-credits sequence of sorts. Starscream is in space (in Protoform form, thus providing reason for a Protoform figure), escaping Earth after his Decepticons got massacred. Muttering to himself, swearing revenge and all that, he notices a number of objects approaching. He's somewhat confused at that. They come into view, and we see they're more Protoforms. One of them transforms upon seeing Starscream, and (bum bu BUM) it's Soundwave. He says something cool, and the film ends. Again, with no real evidence as to ANY after-credit sequence, it's all speculation. Still, it'd be sweet to see.