Gazmo:
I think that LHR will do fine, will do just as well as BFS route did and maybe a bit more profit. Gatwick will take a while to establish and will be tight enough, though my guess would be that Gatwick numbers will grow significantly overall as a result of the extra capacity. easyJet might feel a bit of a pinch, lets think back to FR arrival at BHD, EI arrived at same time. So the effect of EI launching 4 daily LHR at that time and FR launching 5 daily at that time on STN was that easyJet dropped LTN STN and LGW by 1 each day so LGW went from 6 to 5 and 4 somedays , STN similar I think went to 4, so if I recall easyJet probably took 3 rotations out per day.
Effect was that overall number grew quite strongly. Again FR had rock bottom fares.
Passengers who are choosing the options of winter city breaks may be attracted to London as opposed to some of the Euro routes, add to this easyJet have cut back on some routes over winter compared to LY, and EI's own Euro routes have been withdrawn so I would imagine London routes will see a nice boost, particularly LGW.
I believe EI will perservere for as long as it takes to make LGW work, the sun routes will be a good money spinner and this is so strategically important for BHD, so EI need to make this work...