I don't know if there is less business traffic from the Shannon region. While the overall economy of Cork's catchment area is larger than Shannon's, there is a larger number of US multinationals based in the mid-west.
However, if/when open skies between Europe and the US becomes a reality, I don't know if the standard thinking about business class pax will hold. They used to be the mainstay of European routes; now Europe's most profitable airlines don't offer business class.
That said, I can't see T/A out of Cork before 2008.
I'm not sure there's much sense in planning around a route being flown in a 757. We'll see fewer and fewer of these in the world's skies in the coming decade. It may work as a stopgap, but if the airport's management is serious about attracting T/A traffic, they'll need to plan to accommodate the A350 or B787.
Taking a look at this brochure for the 787; the situation doesn't look too bad for East Coast services in a 787.
http://www.boeing.com/assocproducts/...87brochure.pdf
Realistically, a scheduled service to New York or Boston and some charters to Florida are all that is likely to happen.