Actually, we've already done it. A few years (5?) back we had seasonal service to Ireland (I should have saved the timetable). For that matter, many of our narrow-body crews are well experienced, as they spent time on the Mighty L-1011 doing international.
As for the other carriers - I don't really know, but I think it will take a while for them to gain approval for RVSM, MNPS, ect. on their ops specs. They've probably already got Class II nav, but it's a bit of a different ball game over the pond and in the rest of the world. No offense to the General, but does anyone else remember the diffculties Delta had when they started trans-Atlantic? It's a big step up from domestic - no one is watching out for you, and _everyone_ else is counting on you to get it all right, the first time, everytime. I'm sure there will eventually be several LCC's doing it, it's certainly not an insurmountable hill, but it's not something you just turn on overnight.