(Ex-RAF) Manston Airport in Kent would have been an imaginative alternative. Very long runway, loads of undeveloped space, huge number of potential new and local jobs. Might also have seen off the chancers who want to develop the airport for non-airport use and a quick buck.
Wouldn't be surprised if SASTA's shenanigans scuppered Gatwick's chances at the last moment. Without a fit-for-purpose public transport link, you're a bit snookered really.