I would agree with FRatSTN, and in my view the improvements at STN point to realistic expectation from the owners that long haul amongst other services can be sought.
STN makes better sense from a catchment point of view ie reaching further into East Anglia and East London, and also Cambridge of course. As noted, LTN is in closer proximity to two existing EK catchments.
I could see EK adding a new London airport if they want to grow. LHR slots aren't readily available without great cost, which leaves either adding even more services at LGW or trying to grow the market even more by spreading elsewhere
If EK are in 'serious discussions' with LTN, I would suspect it is purely to leverage a better deal from STN.