Why should getting back from the US be such a problem? Ideally for those travelling to SNN a stop on the eastbound journey would be the most convenient. However, you could travel direct to the eastbound destination and return to SNN on the westbound which is stopping for preclearance, provided arrival/departure times allow of course, not much different to connecting to Aer Lingus or CityJet if connecting through LHR or CDG as currently has to be done.
I agree if SNN could make itself a European hub then they could be onto a winner and I think that is what they should have been looking to try and establish. Don't think there is much of a chance of the two Irish airlines working together in this respect- RYR to provide flights to SNN and EI to cross the pond
