There are options open to Aer Lingus other than an extra aircraft or a W from Dublin.
They could operate their SNN routes as Ws from Dublin, adding capacity to Cork. The fact that this isn't happening is a real sign of how far we are from Aer Lingus expansion in Cork.
They other possibility would be to operate an existing ORK route as a W from Dublin to create capacity. Options are limited here. LHR is out (apart from moving frequency from Dublin to Cork) because of slot restrictions. The same applies to the morning AMS service. That leaves Munich, Nice, Paris, Barcelona, Brussels and the evening AMS service as possibilities. Practically, if it happens, it'll be with one of the routes that is served 2-3 times weekly, not a daily one.