Francis, do you realise that the hold areas on the ATR's are in front of the cabin and also in the rear, not under the floor like on larger aircraft? They appear to be more than adequate. There is no issue that I have ever heard of with baggage (connecting, or otherwise) with the ATR. The overheads for cabin baggage are tight though.
I think for ORK-DUB to work (which Im skeptical that it would) they would need to trade fairly heavily on connnections, for effective connections to North America and allow for day returns three daily services would probably be needed. Something like an 0700 departure from Cork, with an arrival scheduled for 0800, or so, departing DUB at 0830. Maybe the aircraft could route
ORK-DUB-ORK-BHD-ORK-DUB-ORK, killing two birds with one stone there, not sure if there would enough traffic though. The final possibility would be for two aircraft to operate in a triangle via a common UK airport. If EI and/RE wanted to operate on ORK-DUB there are a few ways to make it happen, but Im not sure the market exists as it once did. The trains and roads are much better and getting through airports quickly is more difficult.