Alright, I've been thinking, and I have a new guess for traitor.
I think its Nick Fury. Only, he doesn't see himself as the traitor.
Lets look at it this way. Gunnar was hired by Fury to spy on Thor, then Fury would have heard the comment about the super people, or at least tried to put two and two together from Thor's one-sided conversation. Fury gets a little too paranoid and starts taking down all the people in the Ultimates that he doesn't have complete control over. Each event was orchestrated by him, made to look like his involvement was more coincidental than it was. Gunnar may or may not still be Loki, but this could be how on of the Ultimates is still a traitor.
I think that Hawkeye may still be a real attack, one that Fury wasn't involved in. And the aim of that attack was not to send Fury a warning, but to get Fury to take down the one person he thought he could always trust: Captain America.
Including the annual, this may also be an attempt to stop the arms race before it got too far. He tried disabling his team to send a sign to other countries that the super people aren't as unbreakable as they may think. This would only be more reason, as the annual was claimed to not be needed.
In a final note, the team Volstagg warned of is actually this new villain team. He was being more cryptic than Thor expected. If Thor is psychotic, that would explain this. Sometimes, the voices aren't very straightforward.
As for Black Widow, I hope she changes sides just so she doesn't get killed. And whoever mentioned that the cover of #9 could possibly be Tony commiting suicide, I thank you for your innovative guess.
My guess for the villain team is:
Abomination
Gunnar (Who traded sides after being assigned to guard the harness, but not the hammer)
Ultron
Red Skull
Unknown Character A (Goliath or Executioner?)
Black Widow
Unknown Character B (Enchantress?)