I am pretty sure one of the first (if not the first) transcontinental flight that gets resumed at SAN will be to LHR by BA. There is no question of whether it will be resumed, only when. JL also had carved out a niche for itself at SAN; and with LAX becoming less of a connecting hub for AA, I am sure NRT-SAN on JL is just a matter of time, especially given the massive OW FF base at SAN from AS.
Sure one day maybe, but SAN is hardly a market for either BA or JL in the grand scheme of things.
Its pretty apparent what the priorities for each airline are now during COVID. According to airlineroute.net both BA and JL have added more service back to the US in the last month, but obviously not SAN.
To maybe put this in a clearer perspective, AA-BA had 5 daily flights between LAX and LHR including 2 A380s. Today they are down to single 789. The market has to return massively to place like LA, before SAN becomes a priority to add back.
Is SAN an approved airport for international arrivals during Covid-19? I remember back in May the approved 15 airports are:
Boston-Logan International Airport (BOS), Massachusetts
Chicago O’Hare International Airport (ORD), Illinois
Dallas/Fort Worth International Airport (DFW), Texas
Detroit Metropolitan Airport (DTW), Michigan
Daniel K. Inouye International Airport (HNL), Hawaii
Fort Lauderdale-Hollywood International Airport (FLL), Florida
George Bush Intercontinental Airport (IAH), Texas
Hartsfield-Jackson Atlanta International Airport (ATL), Georgia
John F. Kennedy International Airport (JFK), New York
Los Angeles International Airport, (LAX), California
Miami International Airport (MIA), Florida
Newark Liberty International Airport (EWR), New Jersey
San Francisco International Airport (SFO), California
Seattle-Tacoma International Airport (SEA), Washington
Washington-Dulles International Airport (IAD), Virginia
Above list is from DHS website. I have not heard any update yet. So I assume above 15 airports that was approved by DHS in May have not been expanded to SAN yet. So if that is case, I don't think your current assessment can be valid. As there is possibility that BA and JL both want to return to SAN and see it as a priority but DHS does not approve SAN as an international getaway airport for Covid-19. Of course if you quote something directly from BA and JL saying they are no longer interested with SAN then I would think you have some merits in your conclusion. Or if you can find out the new DHS list that have SAN included yet BA or JL had not shown and interests in returning, I would admit you are genius too.