This thread has been drifting all over, so maybe my belated comment is useless?
I think it is a great idea to develop a non pressurized single engine turboprop. Whether ist should have 300 HP (as in the Rolls Royce option, my preference) or 450 is open.
If it delivers decent fuel efficiency betwen FL100 and 200, the price delta on Jet fuel vs AVGAS in Europe and the poor availability of AVGAS in certain countries will make it a great alternative: superior economics, superior reliability, superior comfort and the cool factor of turbine makes for a vey attractive package.
I think Diamond are right in avoiding to "simply" clone the SR22.
Going turbine is a great way of beating it, especially if the plane can become a 6 seater.
It should definitely have a retractable landing gear. This is probably worth 15 KTAS or so beyond 200 knots , so the payoff is huge. And the R&D effort is minimal since the DA-52 is a retract...
Final comment: if Diamond or anyone else come up with a new turboprop, could you please do your homework and design the frigging plane's CG envelope to do away with the stupid pinocchio nose? A few ugly square meters of wetted area that have no other use than demonstrating compromised design work...
Aircraft that are not designed from a blank sheet of paper are too heavy (bye bye payload) , too slow (bye bye range) and UGLY (bye bye coolness)
Look at the Panthera for a proper design from scratch...