When speaking to some of my colleagues in DUB last year they said they and the DAA were going to try ammend the proposal for 3,600m, whether that's still the position I'm not sure, but they believed there was scope to do this in the existing planning permission granted?
3,600m should be possible but it will boil down to the daa footing the bill for the extra length or trying to convenience regulator.
There will definitely be a new application to over turn usage or runways between 23.00-07.00. Can't remember exact limits but the even runway could not be used between 6.00-7.00 and movements between 23.00-07.00 were restricted to either current levels or not much more.