Does it have to be turboprop?
A true combi-BAe146/Avro RJ (the QC version can't do mixes of passengers and cargo) with modern, powerful engines (bringing it down to 2 would be nice) would be pretty slick.
Some leading edge devices too would really help the STOL as well.
Be a little quicker in the cruise than a Herc too.
I've seen one of these up on the Russian 'side' of the Artic - Something like this would be awesome.
