Island Air - it was made very clear to me by Tom Keegan that we're talking at least one to two years at best until the CAA certifies Oban as a public transport airport. In addition, the fire equipment needs to be upgraded and even more important a management structure has to be put in place by the local council ... this doesn't exist at present!
Next, how much do you think a DHC7 is going to cost to operate?
As HugMonster said, airlines select aircraft for routes, not airports. So whilst a DHC7 or F50 might be fine for Oban - GLA/PIK it certainly wouldn't be viable for Oban - Mull or Oban - Colonsay, for example! So on those routes you have the much higher operational costs per seat that he came up with - and I'd be interested as well to see your projections for the overall hourly cost of an Islander!
Bottom line here is that Oban may well have a lot of potential - but it's going to take a lot of time, effort and money to realise it.