BA tried LGW-NQY and it was flying a fuselage full of little more than fresh air most days
Yes, but SZ was running competitively priced thrice daily services to LGW and FR to STN (once daily I believe). There will now be just a thrice weekly SEN service - hardly regular competition and on the other side of London.
Nobody ever said LBA would happen (and even if it did, never thrice daily - 'why wouldn't they just shove more frequencies on the other domestics?', came the regular protest) - yet since BE pulled out of LGW and the BM slots have been inherited it has happened.
an utter waste of a LHR slot in the mid afternoon long haul departure period
Of course I wouldn't expect anything regular or business orientated, but if BA can serve LBA, IBZ, PMI as well as the charters out of LHR then I see no reason why NQY doesn't stand a chance. Nobody ever said LCY would get its IOM route. It did, and on a Saab 2000... whoever says they saw that coming is telling a porky.
It might be unlikely but certainly not 'no way'.