Millar, when talking about Vol. 2 for the first time, said that Captain America would open up the new chapter in the Ultimates on a reconnaissance mission in Iraq, where he would irradicate a terrorist faction. I do remember seeing this as well as seeing stuff about marriage, someone getting shot in the head, and members swapping.
I'm getting the feeling that Giant Man will be the one that will be joining the Defenders. If that's him on the last preview page where the phone is ringing, I'm almost positive he's getting reassigned to another team. Millar needs to have him around, you know? It would add to the drama and tension of the title.