Personally i think that there is a lot of possibility for Longhaul ex LGW, Virgin & BA already have a token Longhaul network, but the problem as
Skipness says is the feed.
Take BA for example, I very much doubt they would expand Gatters currently due to the probable take over of BMI and the slots at LHR that would give them.
However, if they were to send an extra 5 7772s to Gatwick to operate more longhaul routes they would need feed, the Gatwick shorthaul route network is lacking in UK Domestic routes (some are covered by BE) as well as very much lacking in Europe, BA doesnt even operate a Paris route from from LGW, let alone German and Spanish !
cs