Hi,
Great news, and a great strategic move for Aerlingus in beating EK to it. I doubt Baltimore will be sacrificed though: it is doing well as far as I can see, and bear in mind that EI were very quick to return to it once the 9/11 situation began to stabilise. I'm sure a 330 can be picked up from somewhere! EI has also leased in aircraft before for the US operation in the summer.
The only thing that might suggest BWI being dropped is if US are doing so well on Philadelphia that they are managing to steal enough traffic from EI.