depends how the storyline goes, it could be part john and kate emerging from the bunker and round up others fighting skynet etc fast forward to the more advanve machines being cranked out all out war ..and infiltrators beihg built.
frankly for the 600 and 800 we wont be seeing any major roles for the human exterior, mostof them fight unskinned, u could have many unknowns for the infiltration scenes ie in t1. unless the story goes on how john captures a few machines and learns how to skin them etc sending one back to protect his mom, and keeping some to help him fight the others etc, then u might want a major actor for one of those, vin diesel! no van damn please!! was a van damn fan when i was younger ,,how the man pissed away his career!
i once saw e hollywood story on him, something about his drinking and his marriages etc etc affected his career and hollywood didnt wanna pursue to take him seriously after that, i think during the 80's he was makinga lot of waves and there was a possiblity for him to become an A list but then it went downhill, does he even act anymore???? gone are the days of bloodsport and kickboxer!