Not if but When and Who !!!
BRS -New york B757 with y150 pax is easily achievable.
We have had in the past (fact) had direct flights from Bristol to Orlando with By 767-200's (y273)in 1997 and AmTram B757's (y215 and direct- I used to file the the fpl's ) also to Orlando in 1992.
The key is the market in terms of potential pax. If we didn't have some of the best aerospace , IT , Drinks ( Cider !!) and Defence companies in the world then we wouldn't stand a chance , as it happens we do everyone knows it including the US carriers so as I say not if but WHEN!!! ( and who ).