Safe to say you can choose from any of the current Aer Lingus routes operated from Cork, where Ryanair do not currently fly to from Cork.
I'd bet on a Brussels link reinstating the route withdrawn by Aer Lingus. Then choose from any of the gaps that exist:
Amsterdam, Barcelona, Palma, Dusseldorf (Weeze) or Cologne to target the new EI route, Palma, Munich (Memmingen), and take your pick from Birmingham or Manchester. Ideally, they would add capacity to Eastern Europe and I'm guessing another based unit at the airport.
EI-BUD
BRU won't happen.
They fly to Palma already?
BCN is unlikely imo considering it would really be a summer route.
Cologne, possibly.
Memmingen nope.
BHX/MAN nope.
Eastern Europe is very likely IMO, likely a polish route or two. (KRK is continuing from SNN for the winter at least, doing very well)