3 Abreast seems most likely for such a small seat count meaning a cabin lenght of about 14 rows x 30 inch = 420 inch or 10.5 meters.
4 Abreast (maybe frontal area / drag is less improtant for a slower prop 12 rows 360 inch 9 meters.
Engines : modern scimitar props and 2200hp per engine.
High wing to ease quick (de)boarding.
Maybe a modern smaller/lighter ATR/F50 kind of design.. Maybe double bubble to avoid the typical luggage issues of existing RJ's.
Max speed 340 mph (540 km/h) ? Range 2000km / 1200nm?
Maybe the DHC-8-200 is an oldish heavy shrink?
Goal would be to keep OEW under 10.000 kg
