Licensed Runway Length
I'm fairly sure all you would end up with today at Sheffield is a Code 2B runway which will stretch to licensed lengths of 1199m max (3,934ft) regardless of how much physical tarmac is there now or could be added at either end.
Runway length simply dictates everything when you are down at that level in terms of commercial opportunities.
Sorry, but that isn't enough to do anything serious on the regional airliner front or business aviation front.
Whoever is wishing for all this is completely blind, ignorant, misled or arrogant.
Do the runway performance assesment, please, before taking this any further. Confirm the above, ask the 'experts' what aircrafft can use that length on an AOC/commercially, and how many passsengers and how much fuel you can get out AND IN - it's the landing weight constraints that will kill most dead.