I'm not sure what the history behind it is, but certainly Ryanair have been very agressive in going after some of RE's more profitable routes. Aside from the PSO Dublin-Kerry route, we've seen Ryanair start the following, which would have had an impact on some RE yields
Cork-Dublin
Cork-Prestwick & Shannon-Edinburgh (RE have Cork-Edinburgh)
Shannon-Leeds Bradford (RE have Cork-Leeds Bradford and had Galway-Leeds Bradford)
Cork-Carcassonne (Not a direct RE competitor, but it will have taken traffic from various RE tourist oriented flights to France).
If they end up with spare capacity at either base, I wouldn't be surprised to see them go onto Cork-Belfast City as that must be one of RE's most profitable routes left where there isn't a serious runway restriction preventing FR from going on.