Footster,
But Roborough would always be handicapped by it's short runway, airliner operations shall, literally, always be restricted to a home based, or local, operator and every other airliner, biz jet, or whatever that goes to NQY or EXT because they cannot operate in/out PLH shall always be lost potential and lost revenue.
If there really is a requirement for an airport in the region then someone should buy up some land, with planning permission, nearer to sea level, perhaps to the east or south east of Plymouth, where nobody wants to build houses, and build a circa 6,000ft runway airport from scratch.