I'm not convinced about the 319 for EI, as it was envisioned above. One less cabin crew and 30 less seats is hardly worth it.
*cough* easyJet seem to manage OK.
Unless you think a whole new manufacturer and training set up would fit the bill. If they go for the ERJ would Aer Lingus mainline fly them or would they be operated by RE? Perhaps EI own the aircraft, routes and licences, RE supply the crews. I would be surprised if EI mainline got a look in on a smaller aircraft. Before anyone shouts "Jet Blue" they have the dynamics and growth of a start up, not a damaged legacy in a mature and contracting market.
Given the A330 is too much aircraft outwith the summer peak, I agree that the A350 is not a good move.