FR looked at using SNN for transatlantic last year. The plan was to feed passengers from all over Europe into SNN to North America using the pre clearance in SNN to enable them to use the regional airports in the states. Given how tight they are capacity wise in Europe already, and that these aircraft would be making 2 flights a day transatlantic as opposed to several rotations a day in Europe with their 25 minute turn arounds, aswell as range restrictions on the NG, they decided against it. This may change when they get the 737 MAX.
I would be delighted to see ORK get a Westjet service, fingers crossed