The only way that Aer Lingus are being encouraged into Shannon is probably that lower fees are being charged for restarting the route there. If Shannon's fees and Cork's fees were the same, there may have been a case for just adding frequency in Cork. Cork Airport always has the option to change the fee structure to encourage airlines to grow routes as well as add new ones.
I'm not especially impressed by how late Aer Lingus are removing/changing the flights to Barcelona and Munich, even if I'm not personally affected. It's one thing to make these changes six months in advance, but they will have a lot of passengers booked on those flights and with accommodation arrangements made etc.
Regarding Copenhagen's ORK-AMS-SNN-AMS-ORK suggestion: I could see Ws being operated out of Cork, but for that particular route, I reckon NOC would make a better option than SNN. For all NOC's expansion lately, it still doesn't have a hub connection. I also reckon that in the summer schedule, ORK-AMS could be supported 17 or 18 times a week, if Aer Lingus wanted to do something like that. Unlike SNN, adding frequencies to NOC doesn't take from Cork's passenger base.