China Southern Airlines did indeed announced Wuhan to LGW prior to the pandemic. Very much a potential airline for LGW.
Delta as you rightly pointed out planned to operate BOS to LGW prior to to the pandemic. I agree with your assumption regarding the reasons why they might eventually fly that route.
I also agree with your comments and the reasons regarding the return of CX to LGW
On another note.
Air Asia X have gone completely silent on their proposed return to LGW with their planned KUL-DXB-LGW routing. I was very skeptical from the very beginning when it was originally stated that the airline was planning to make a possible return to LGW. Although it would make a great addition to the ever growing long haul portfolio at LGW I still remain very skeptical of the return of Air Asia X.
On another note.
The newly formed Ghanaian flag carrier Ghana Airways are to receive the first out of of three B789s on order from Boeing in the Q3 of 2023. The airline has stated that they intend on initially using their B789s on opening up long haul routes from the Ghanaian capital of Accra to London LHR and New York JFK. If the airline are not able to obtain slots at LHR I'm certain that Ghana Airways could well be another potential future long haul airline at LGW.
During 2022 the Tanzanian flag carrier Air Tanzania announced that they were intending to resume flights from DAR to LGW again once that the airline can obtain slots. Air Tanzania had obtained slots for LGW in 2019 for a resumption of their Dar Es Salaam flights which were supposed to commence in 2020. Obviously the pandemic changed those plans and those slots at LGW were lost after three years and the airline has recently had to reapply for new ones.
Air Tanzania are due to receive their third B788 added to the fleet soon giving them a total of three. Air Tanzania have also just recently received a new build B767F direct from Boeing with cargo expansion on the airline's radar. Air Tanzania could well be another potential future long haul airline at LGW.
Air Tanzania would be a very welcome return to LGW. On a personal note I can remember being on the viewing terrace at LGW in July 1980 when the first ever Air Tanzania Boeing 707 landed on it's inaugural flight from Dar Es Salaam. The livery looked great on the B707 along with their leased Ethiopian B767s. Their current livery looks great on their B788s and hopefully we will eventually see them at LGW.