There was a rumour a while back of a 2 x weekly TCX to Cancun, nothing came of it though. I suspect carriers who would think of launching this service are already getting Irish pax through MAN, LGW etc so probably not worth their while in doing it.
On a different note, I've noticed a B764 doing the Delta DUB-JFK run lately, a permanent fixture or just for the web summit last week?