Nicking traffic was always a danger. But if we become one big happy functional airspace block there would be no reason to nick the traffic, would there?
Anyway, I always thought the 'nicking traffic' argument was a bit misleading as any traffic entering Shannon's NOTA, with the exception of Irish inbounds, would have to fly through UK airspace anyway. The Irish would have to give the service away for free to make it worth while for an airline to make a big detour.