Agree that the most likely carrier to start US/Cork flights would be a US carrier not flying to Shannon and the only chance of an Irish carrier coming on the route in the future would possibly be Ryanair if they succeeded in getting a deal with Boeing on an order of 737-900's or 787's
Ryanair would be using B767 on US routes. They plan to buy up many once other carriers switch to B777,787,A350/A380. The will only be ordering short haul aircraft.