Collapse in traffic.
At least it would stop airlines from pocketing airport charges when passengers don't turn up. However that would probably make routes less marginal.
It's obvious now that the phenomenal growth at Irish Airports was builit on Celtic Cubs making multiple trips around the UK and the Continent.
Lack of inward business particularly at SNN and ORK is now costing them dearly. There was far too much emphasis in marketing outbound Sun routes and not enough emphasis on attracting incoming tourists.