The facility will enable airlines to fly into cheaper, secondary airports in the US and whilst the population of the SNN catchment area itself isn't large enough to sustain multiple services linking SNN with these airports, if passengers from Europe could be fed into SNN to connect to these flights, it could work.
But why not just develop such a hub in Stansted, Dublin, Bristol, Birmingham where you have a larger local population?
Pre-clearance is't such an advantage is this set-up. What's the idea? You get off your Hahn - SNN flight, go up to the pre-clearance area, board your SNN - Buffalo flight. What about when your Hahn - SNN is delayed a bit, and you're rushing to your SNN - Buffalo flight, which then you miss due to having to pass through preclearance...
