I can't imagine the airport would want to see Gatwick Express as a brand disappear, given Heathrow, Stansted and Luton have such services under the "Express" banner. Neither really should it. As pointed out up thread, "Luton Airport Express" continues on to Corby so by that logic should it be renamed Northamptonshire Express?
Binning it altogether to make way for more trains may well be prudent in future if that's a possibility, but even then I'd still expect some services to be branded as Gatwick in one way or another. The Gatwick Express services, despite omitting East Croydon and Clapham Common calls, don't really yield that much of a journey time benefit from the airport to London Victoria anyway.
The main reason in my eyes for retaining an "airport express" subdivision is not so much that it offers a premium service, but one that is specified specifically for airport traffic, eg additional luggage space. Granted that doesn't warrent the fare differential which is the main issue at stake, but if you lose the airport subdivision altogether, you risk conflicting needs on those services in future. Having the Gatwick Express separate from other Southern services essentially safegaurds those for airport traffic as the priority customer base. Take Greater Anglia as the example where the 745/0 intercity's have first class, buffet service and table seating, whilst the 745/1 for StanEx omit those (albeit these are being fitted with tables for resilience to cover 745/0 duties when needed) and instead have additional luggage space. If Gatwick Express were to disappear altogether, how would you differentiate these kind of specifications, particularly on any future rolling stock that might replace the current configs?