Another option could be to complement the Aer Lingus Brussels service by increasing the frequency with services on the ATR72. Ditto for Paris.
Aer Lingus Regional certainly have a lot of options ex-Cork.
At a guess, the block times for ORK-BRU and ORK-CDG would be between 2 hours 15 and 2 hours 30 in an ATR - quite a bit longer than the ATR "sweet spot". So I don't think the economics work, not least because Aer Arann would be unable to get 8 sectors a day out of the aircraft so they'd only have 6 sectors worth of revenue from which to pay their new aircraft's leases. In choosing ATRs over Q400s Aer Arann made a clear decision that their core market out of Ireland would be UK only, not continental Europe.