I would not allow Aer Lingus and Ryanair to start flight to Northern Italy.
As Cork is a publicly owned airport, I don't think this would be legal.
As for expansion...
The best opportunity is in Aer Lingus basing a 5th aircraft.
AFAIK loads and yields out of Cork are better than Dublin or Belfast at the moment, which would seem to put Cork up the pecking order for a new aircraft. However, as noted by other posters, the Gatwick situation muddies this somewhat. Also because of the T&Cs, Gatwick and Belfast have lower cost bases.
If EI did base an extra aircraft, I would imagine it would primarily be used to expand services on existing routes. BHX has scope for more services as does CGD. AMS could go double daily in the Summer as well as the Winter and could probably even go to 3x daily on Thursdays, Fridays, Sundays or Mondays.
If capacity was left for new routes from EI, LGW would probably be on their agenda, even with FR on the route at the moment. FRA and a return to MXP or MAD would be possibles as would taking up the GLA route. Adding an extra destination in the Canaries for the Winter and maybe somewhere like PMI in the summer might also happen.
If worst came to worst with RE does anyone have any thoughts on what might happen with the BHD route. There's money to be made on that route at least.