I don't think there's a chance of Aer Lingus going down to daily. At it's busiest, the route handled a couple of hundred shy of 180K per year. Last year it was 155K driven by capacity cuts.
The KLM service is only introducing 46K new seats, so it's largely going back to where it came from.
Even if it did go to one Aer Lingus in the morning and one KLM in the evening, A 15:50 departure ex Amsterdam isn't exactly that terrible for someone traveling from Cork on business. Timings are a bit more problematic in the opposite direction, but the bulk of the business traffic is ex Cork.
As I said, none of those summer rotations were unprofitable (and I have seen the figures, although admittedly pre-2012). It was more that there was greater profit to be made elsewhere and to an extent because the 21:30 arrival represented poor aircraft usage compared to what Aer Lingus look for now. That's too late to send the aircraft out again, but represents 3 hours of non-used time during the day.
Also as I said, KLM know exactly how much connecting revenue they were losing out on as a result of the evening rotation not being there. They have precise figures from a few years ago and should Aer Lingus respond by dropping frequency, I have little doubt that those figures would justify an increase in frequency for them.
The risk that Aer Lingus are running in Cork now is that if they become just London + Leisure they leave themselves very exposed to Ryanair who have greater flexibility and the ability to undercut them everywhere.