The more I think about it, the more I don’t understand why airports with Schengen preclearance aren’t a thing.

Traditionally, US preclearance was easy to do in Canada because 90% of its international flights were to the US.

I don't think even Britain has that big a share of its international flights bound to Schengen. Maybe some low-cost London airports...

With the traffic level precedents of DUB and SNN, though… we should be talking about any reasonably large GB/IE airport other than LHR/LGW.

And from the NA East Coast, all flights to the EU leave in a short window about 3-4 hours long. Don’t even need a full-time station.