At the end of an interview with Film Journal International, Terminator Salvation director McG offers some surprising hints about what he is thinking for the sequel. "I strongly suspect," he says, "the next movie is going to take place in a [pre-Judgment Day] 2011." He goes on in detail:
John Connor is going to travel back in time and he's going to have to galvanize the militaries of the world for an impending Skynet invasion. They've figured out time travel to the degree where they can send more than one naked entity. So you're going to have hunter killers and transports and harvesters and everything arriving in our time and Connor fighting back with conventional military warfare, which I think is going to be f******* awesome. I also think he's going to meet a scientist that's going to look a lot like present-day Robert Patrick [who famously played the T-1000 in Terminator 2], talking about stem-cell research and how we can all live as idealized, younger versions of ourselves.
None of this is set in stone, of course. It does suggest that the Terminator Salvation plot line will be wrapped up enough to leave the post-apocalyptic world behind for a while. And since this is to be a trilogy, it would leave open the question of which world, and which time, the final installment would be set in.