You might be surprised, transatlantic operations out of GLA are set to increase this year with rumours of a daily Boston, on top of 2 Newark, the Chicago and Philly flights plus the usual Canadian Destinations. Emirates are allegedly going to go to 2 daily (the second to meet up with the Sydney departure in Dubai).
Virgin could easily base an a/c in GLA and run Boston, New York, etc and make a healthy profit into the bargain.