There is NOTHING to stop EI operating a ORK service to JFK even after the move to T5 - T5 is getting an international wing, which will have customs and immigration facilites.
Not having a dig at Cork or anthing but common sense is stopping the EI CEO from operating a ORK-JFK service. Aer Lingus are a demand lead airline who need to make profit and need to maximize revenue per passenger and having a Cork and Shannon service will not do this.