Re A330, Dulles and any other base
You need to understand that AL is a seniority based airline. That means that in order to change fleets, seats or bases you need to have in a bid and for it to be accepted by the company. These are taken purely in seniority order at the time the bid closes out. If someone ahead of you on the seniority list doesn't want to bid for something then your number may well come up. There are also base freezes which the company imposes on you.
The only exception to the rule is when it is in the interests of the company to drop any freezes to fill up seats.
I would hazard a guess that the Dulles base is now over a year old. There was very little interest in anyone moving across at first as generally the T&C's were extremely poor, particularly on the FO side. The company went down as far as the most junior FO on the ROI seniority list before it got the numbers it needed. There are rumours of a 2nd aircraft going in there shortly. We don't know whether this will be filled by ROI pilots or if UAL will get to fly it. Another unknown is how many FO's would now consider shifting to the US in order to get 330 time and get away from the recession and quite possibly the mother of all budgets looming. Taxes could quite well become prohibitive in Ireland with the IMF in town. It would be generally fair to say that morale is low amongst the FO's with very very long time to commands coupled with poor pay and conditions and continuous industrial relations strife hanging over their heads. Therefore getting on the 330 in order to improve your CV could well be seen as a sensible way out for many. Time will tell.
Unfortunately your US visa is worth nought unless your seniority number comes up.