Links Air will soon be carrying numerous passengers to the IOM TT, after which there should be a smattering of holidaymakers along with regular business passengers.
I'm not sure whether or not it will prove a success long term, but it should be fine for the next few months. I hope so, as I'll be a regular during July and August.
Eastern used to fly Jetstreams to the IOM from Birmingham, Newcastle (and I think Edinburgh). As you don't need many passengers to fill a J31 I imagine that the Doncaster routes could be made to work. The key is good marketing.