If they put parking across the runway, they may be obliged to provide buses to the terminal. I can just imagine the anouncement on the planes.
"As Cork is a self-marshalling airport, we ask passengers to watch out for the A320 that is taking off as they're walking across the runway..."
Seriously, apart from the purchase costs, what would be the issue with the agricultural land next to the cargo area. It should still be relatively flat at that point.
I love the typical Cork weather in the photo.
As for B747s. I can only remember 2 landing at the airport ever. There was a Qantas charter a couple of years back. There was also a KLM flight from Aruba to Amsterdam that made an emergency landing at the airport.