This is all very interesting and no doubt factually correct, but efficient aircraft are meaningless if pax don't want to fly them. I know that many pax don't care what the plane is (and some actually prefer flying props), but a significant number of (particularly biz) pax will choose a real jet over a barbie jet and a barbie jet over a prop. So that effectively leaves the realistic market for props to very small markets where the competition is RJs only. And as traffic grows over time, there will be fewer and fewer of those markets.