Why won't Norwegian use pre-clearance in Dublin? Sorry if I missed this explanation earlier
To have operate from T2 to have pre clearance, unlikely given current demand that they will.
There is no doubt Norwegian will stimulate demand with low fares, but there are literally 100's of points in the US, and a significant portion of passengers who fly Dublin US are not originating their journey in Dublin or ending it in their first US port of entry, e.g. passengers coming from BHX to DUB and are onwards to EWR, equally pax starting in Denver going to MAN via JFK, so without this connectivity they will need to be consistently very keen on price to develop these new points, it will take some time and resource to get it right.
They are starting flights from Ireland to USA, and the incumbent carrier is probably one of the most experienced airlines on the North Atlantic, who is also ahead of its peers in terms of operating costs. They will get a run for their money, the US carriers in particular will retaliate and are nimble in that regard.
Finally, with them only having 3 aircraft (738's) certified to fly transatlantic, is it likely they will serve all of ORK, SNN, DUB and BFS. My guess would be that DUB will come last. ORK was the headline airport, then they talked about SNN and in the interim the BFS opportunity came along. So hard to see how they will do satisfy all of that with 3 units. They could sweat that asset and increase frequency and fly more than 14/15 hours per day... though unlikely...