If it's the ideal compromise, how come 110-150 seat airliners have sold so poorly? The Fokker 100, B737-500 and -600, the A319, the 737-7MAX, the MD-95 (B717)--all a bust. I submit with today's labor and infrastructure costs; planes of 100-130 seat range cannot produce enough revenue. The Fokker had the highest CASM at American, probably at USAir, too.
GF