i can only guess that some A318's could be ordered to expand the LH services ex LCY as these services are crewed ex LGW, so perhaps they could be delivered in all J config.
If they were going to go down the all J model I suspect it would be out of LHR, the current focus and business model at LGW is more leisure, in both long and short haul. The A318 *may* be a good bet for short sectors which need smaller aircraft on some days to maintain frequency, offsetting the higher weight of the aircraft, versus models that weren't shrank from a bigger aeroplane! Bear in mind there were a few routes that *seemed* to work on the B735 that were closed when they went all B734. It all depends on how the numbers stack up. If they want to grow the BA presence profitably then I would have thought BA CityFlyer would be a good option, but if Gatwick gets new A319s / A320s to raise their game against Fortress Orange I will be delighted!
There would be a good case for moving G-EUPA (the oldest A319) and her sisters from LHR and sending the new aircraft to T3 / T5 but that's NOT what I think Gatters deserves after losing so much I think. Fingers crossed.