The thing about Portarlington is that it is nearer to Dublin than the current airport! Maybe not at 3am, but certainly during business hours. The train service right now can do the journey in 40 mins. I am sure that a well designed airport could be built, along with upgrading the rain line and a motorway spur to the M7 for the sum that the new DAA terminal is going to cost.
Trouble is, it would make so much sense that everybody would use it - so Dublin, Cork, Shannon and the other regional airports would loose out. This country is a fine example of one that isn't run for the benefit of it's population. The vested interests would never allow an airport to be built in Portarlington, or anywhere else in the midlands for that matter, even though the new Taoiseach is from there. Nor would the DAA or the unions allow another airport to be built in Dublin.