The road on the western end isn't much of a consideration. It's fairly minor and could just be routed around the perimeter of any extension. Of more interest is the fact that there's the remains of a ring fort down there. Extending the runway would miss it, but it could be a bit of a pain for a construction site.
On the eastern end, the Kinsale road would probably have to go below in a tunnel. I've noted before that the access road to the airport takes an unnecessary dip and then rises to meet the roundabout. It makes me wonder if someone has thought of lowering the level of the roundabout.
There are a few other issues on the Eastern end. There are a few houses that would have to be demolished. The floodlights at the Harlequins hockey ground would have to go, which would probably mean moving the entire club.
A slight problem with the runway is that any taxiway (assuming there would be one) would have to go on the side away from the airport, which is undesirable from an operational perspective. Perhaps a new runway could be constructed parallel to 25/07 with the existing runway turned into the taxiway.