Since Open Skies, competition will continue to rise. When do you think the demand will 'saturate'? My prediction is that within the next 2 years, the bevy of airlines serving the Anglo-American market will be significantly trimmed down to only 2 competitors. Namely British Airways and Delta Air Lines (especially given their impending merger and extensive network). My prediction is that it will be as if deregulation never happened on the transatlantic market.
Given the conditions at LHR, I suggest that Virgin Atlantic concentrates on capturing overseas markets. DXB would make a great focus city for them (similar to QF at SIN).
Back to MAN-JFK: given that slots at LHR are a valuable commodity, I'd say that this route wil be put on hold for a while. Does anyone know anything about the business loads from the North of England?