Cranky Flier analyzes the surprise Delta-Virgin merger in terms of JFK–LHR:
Of course, British Airways and American have the strongest position in London by far. Delta would have been hard-pressed to grow a position itself considering the slot restrictions at the airport along with the already ample capacity on these routes. With this deal, Delta becomes more relevant in London, but more importantly, it becomes more relevant in places like New York, from where London is one of the most important business destinations. This simple chart showing daily flights each way from all New York airports should make it very clear.
I told you it was a simple one. Today, Delta is an afterthought. If its schedule fits a loyal traveler’s needs, then people will take it. But more often than not, that probably won’t happen. Combined with Virgin Atlantic, however, there is a very respectable schedule that now also covers the other side of the Hudson in Newark. Delta becomes relevant.
Whatever happens, I just hope there are at least three airlines left standing. That's enough for real competition on popular routes, and none is more popular for trans-Atlantic travel than New York to London.