What i see in this picture (which is awesome by the way, and thank you for posting it), are two G1 vehicles. If there will be Stunticons in TRANSFORMERS 4, I'll be so happy.
I think they learned from last time. At least, I hope they did. Bay and Co have gotten a little bit better with creating threats since ROTF; there were no jokes surrounding the Driller.
Considering how the movies have a huge fetish for evil Primes I wouldn't be surprised if the rusty truck turns out to be Nemesis Prime. After all if it ain't broke don't fix it! <_<
Where did the stunticon rumor start? I'm not to familiar with who they are. I'm hoping the truck is grimlock personally. I'm probably in the minority on that, but think it would be cool.