New ATW story on EI and the A350s:
Aer Lingus CEO: A350 not ideal for carrier's transatlantic routes | ATWOnline
Bottom line: EI will take the aircraft, although they are overspecified for the airline's needs. Won't say how many will be operated and more than likely, will be operated side by side with A330.
I think we can take it from this that any prospect of switching to the 787 is out the window.