Manston was also used as a training site for the airlines as well as flight training by TGA so there could be a few revenue streams coming into play once it's actually open
All the revenue streams listed are the one's in place before the airfield shut. The main arguement of the developer seems to be that they can attract 10,000 cargo movements a year, but no indication as to how. It'll need more than a couple of fresh produce flights a week and the odd ad hoc charter