Agree with the above...MCO is best as a weekly (and during the peak months, we could fill a 747). Add in a twice weekly YYZ, and a twice / three times weekly JFK / EWR and it could make sense for someone to base a single widebody at BFS.
The only airline that would seem a natural is VS. They operate from the regions already (MAN / GLA) and have the infrastructure in place at the destinations (have they started YYZ yet from LHR?). They also have the mix of aircraft...A333/A343/A346/789/744...
Hopefully the flights this summer are a toe in the water. I can't think of anyone else who could do this. The only other one is EI, but I think they stated they weren't going long haul from NI. Unless IAG ownership could change their minds...