You also have to account for "airline mentality." There are very few airlines that can envisage flights that neither start or end up at anywhere other than their main centre of operations. Also, such an operation might also fit into the "too difficult" category as labour agreements might have to be renegotiated. It would also be likely that such aircraft would be flown by 'Junior" pilots as the heros in the 747s/777s and such like wouldn't be able to lower their personal standards and fly something smaller what they currently fly. This would have to be done to get round scope clauses, night flying restrictions, days off etc. and that in turn might make the operation uneconomic. Then you have the "product offering." Would a "business class" passenger be prepared to sit in something like a Embraer 190 for five hours? The economy passenger might actually be better off if some IFE was fitted as the seats are a bit bigger but even then, the aircraft might get a bit claustrophobic.
The right aircraft might be a something like a 737-700 equipped in all business configuration (40-50 seats), with prices to match! Which is probably not what you wanted to hear.