I don't believe that a Cork-Dublin route would be viable anymore and rather than suggestions that Ryanair killed Aer Arann off the route, it was actually the opening of the motorway which killed both of them.
On top of that there is also a high frequency express bus service which has proved to be a very successful. Even the train struggles against the express coach these days.
I suppose the only way you could ever see the route coming back is if Aer Lingus see a big drop in passengers originating in Cork and travelling up to Dublin to take flights not served from Cork.
My own guess is that passengers are getting to Dublin by other means.
I think that using a peak time ATR slot from Cork to a UK provincial airport gives EI and Aer Arann much more profit potential than a feeder to Dublin.