To be fair Shannon is classed as an Atlantic emergency diversion airport so the chances of it ever losing its 24hr cover is close to zero. All I can say about speculation over cover hrs at Cork is I can't see airlines kicking up a fuss, Ryanair do not operate between 12am and 6am, Aer Lingus are only ever scheduled to be as late as 12:15am with the latest this season being an Arkefly flight from Las Palmas at 12:45am. I think theres been one night so far this season a flight has touched down after 2am and it was a delayed Aer Lingus Alicante flight during the Portuguese general strike. As Ryan2000 points out the only problem this proposal faces is when theres delayed flights if they're going to be forced to divert to Shannon well then thats just not acceptable, if the IAA were to pursue say a 1am to 5am closure during Summer and 12am to 6am during Winter but would allow for cover during delays i.e. when flights are scheduled before closure but incur delay and are facing an arrival after closure - Then I believe this would be accepted.