The last part was more aimed at my good friend LGS! I'm sorry if it seemed otherwise
There has been a huge conflict in opinion between us an I can't help feeling a little bit arrogant in a way when news like this turns out, I suppose because I can imagine the shame they must be feeling when its a time to be hopeful and optimistic.
Assuming EasyJet start this growth by summer 2014, I can't see any other London airport really losing out. Remember EasyJet is known for flying to larger and quality airports and in my opinion, their main London bases being Gatwick and Stansted is long over due, yet Luton and Southend will still remain important to them and continue to grow in the longer term.
There could be an element of route switching, and I do think Luton may be more effected by this than Southend (as somebody suggested in the Luton thread, a route like Tel-Aviv is a good example of one that could be switched). What's important to remember is that Gatwick is totally safe where EasyJet in concerned.
Southend serves a sort of niche and more local market (that's why migration of routes from Stansted to Southend rather than operating from both airports highly angered me, and couldn't see that as a widening catchment area). And their recent commitment and promotional efforts there would make them highly stupid to move away now.
Luton could see a small amount of route switching to Stansted and frequency cuts, but at the end of the day, Luton is by some margin already the 2nd largest base for them and with it being their home airport, it's always going to be special and an important part of EasyJet's business.
The airport perhaps most in question was Stansted until today, and this move only emphasises EasyJet's desire to operate a growing route network and volume of traffic at all four of the London airports they serve. And of course the new aircraft order expected to be announced soon gives EasyJet huge potential to do this.