perhaps you are being sarcastic FANS but if not them I doubt they will reduce ticket prices. Airline marketing people can find a way to demonstrate that the cost of a sandwich is insignificant compared to the cost of the fare.
Actually what i think will happen is a sectorisation of London pax . Live North or East STN or Luton, South Gatwick and West or central LHR.
Although BA are often but not always the costlier option there a £30 difference in cab fare from where I live to go to LGW not LHR and STN is pointless as its such a long way and virtually impossible to get to with any certainty about arrival time.
So looked at overall getting a sandwich or not isnt that high on the list of choices about who to fly with