The Do228 wouldn't need to cope with quick turn-arounds, if it carries more pax and gets there faster.
Wouldn't you rather be in an aircraft with relaxed crew who managed to stand up occasionally, or ones chasing their arse for 6 sectors?
The hindering factor is the pax with hand luggage and finding their seat. You are looking at 20 mins realistically - depending on fuel, coaches and generating a loadsheet.
As for the economics, modern turbine aircraft are very efficient and reliable, comfortable and fast. They could even do a triangle route from say Southend, Bristol or Cambridge. If they make the right move, this could make them a solid return.
As you say, price is very important, equally is reliability and customer service. Get any of those wrong and it will be the fastest way to bin millions!