I am a believer in the future of turboprops.
The theory of "turboprop avoidance" is sheer myth. Besides, people will fly any equipment, provided it meets their schedule, price and preferably DIRECT routing. Recently in Toronto, Porter has been a booming success!
Only turboprops have the economics to do this task going forward. Jets, like RJs have had to get bigger and bigger to maintain economic leverage. Turboprops, with a slight speed push, can replace jets on many routes. You only have to look at Horizon canceling CRJ00 orders in lieu of Q400s, Luxair refleeting their EMB145s with Q series...ATR can't accomplish this as they don't have the scoot of the Q400.
So, I love the highspeed high cap concept you have. I agree you'd need to push over M.7 tho..the P3 has a max of 400kts, and the Q400 is only 360, you should hop up the speed on this.
Also, pax HATE entering the AC from the rear and it reduces the chance of boarding with Jetways.
As far as bringing IN teh engines...bad call
. By bringing the props close to the fuse, you're inviting a larger blade pass vibration as the blade tip shockwaves won't have time to abate. Keep them away from the fuse or you'll end up with a noisy shakey fuse. IMOHO
Anyway, this look alot more than just a hobby to you...where'd you do your design training?