Pax Survey
I think the best indication that pax were prepared to use Manston is the fact that 306,682 passengers did use Manston during the EUJet days, over a period of 11 months.
For whatever reason, those 306k pax voted with their bums on seats. The indication is that there is a market out there that Manston can tap. One thing is for sure, if there are no scheduled flights, no-one can book them.