Very Civil Pilot's point is correct. There is too much sea in the catchment area. There's only around half a million people in the area of Kent to the east of Maidstone. Maidstone is considered to be more Gatwick catchment. Half a million total market is unlikely to provide much traffic for scheduled routes outside of the really thick ones. I might accept plans for a small aircraft connecting to Amsterdam/Manchester/Glasgow/Malaga and a frew summer charters to the mega-markets but anything more is pie in the sky, especially now that STN is going to have serious development. And it only takes an hour to get to LGW by road.
Manston will stay as a freight and maintenance base.