hmmmmmmm....
I dont think that Ultron and Loki are going to pop up all at once, and I dont think Thor is going to return to the Ultimates. If the battle between Thor and Loki takes place in issue #5, he's not going to suddenly change his mind about the ethical use of the Ultimates in other countries. If there's a real problem where people need help, and if the EU Ultimates are needed to help stop Ultron, then I'd bet Thor would come back to help save the day, no way he's rejoining.
And Bruce Banner, I'm guessing that the Marvel Poll that asked what miniseries should get tackled next is to see whether people would buy an Ultimate Hulk mini. I think it ended being tied with U. Wolverine for first place. We'll see him soon, I'd guess in a mini-series mid to late 2006, when Ultimates 2, Ultimate Iron Man, and Ultimate Galactus have all wrapped up.
What my guess is that we'll have a slightly new line up by GTA.
-Captain America
-Iron Man
-War Machine/Black Widow
-Hawkeye - I'm guessing we'll see him die too, to mirror 616, and also because he's the most prepared to die, and would sacrifice himself to save lives
-Scarlett Witch (no Quicksilver, im betting the lightning bolt from thor hospitalizes him)
-Falcon- Bet he come in from Black Ops in the second arc
-The Wasp- Im guessing she'll die, her character is the most expendible at this point, and plus it would put the guilt on Hank times a thousand if his creation killed her
-Hank Pym - Not in costume until the end, where I bet he'll don the Antman outfit and then go to normal size while inside of Ultron, sacrificing himself and destroying Ultron.