Fairdealfrank - it's a bit chicken and egg re the traffic demand question. But an airport with direct road links 15-20 mins from a city vs one that is 30-35 mins away....i think there are airlines who would think they could sell that proposition to passengers.
Re the name, there seems to be sensitivitiies around re Sheffield and Doncaster but the airlines will have to look at it for what best sells seats. No doubt Sheffield is the biggest and best known regional town/city, so Sheffield needs to take prime billing to sell seats. Sheffield Doncaster seems right. Of course locals will always know it as Finningley, just like they tend to refer to Ringway and Speke in those places.