If the authorities in the Republic were serious about Dublin Airport, they would build a rail spur from the Belfast to Dublin line from north of Malahide to Dublin Airport and onwards through the Phoenix Park tunnel to Heuston station connecting up Cork, Waterford, Limerick, Galway, Kerry and all the stations along those rail lines to Dublin airport but it ain`t going to happen.
Belfast and Cork should continue to build up their infrastructure to bid for transatlantic traffic and attract more US direct investment to their regions where currently the vast majority goes into Dublin.