What Gatwick needs is a New York connection again and perhaps with the Delta/Virgin Atlantic JV it may be possible in the future to perhaps move one of the Heathrow to Newark flights to Gatwick and those Heathrow slots could then be used by Delta for a new route from Heathow to Salt Lake City
It's not going to happen. LGW is far too close to LHR for New York to be viable. From Delta's perspective, they looked at LGW/LHR-JFK/ATL numbers when they flew both and the upshot was both are now entirely at LHR. As the JV with VS grows, that focus on LHR will only grow. It is not competitve to move drop a key business route demanding *more* frequency to be competitive on LHR-NYC, to open up a new more niche route. I believe LHR-SEA is in the works, but not at the expense of a JFK rotation.