I've wondered that myself. With all the technologies we have, be it Schwintek slideouts that work well with lighter rigs, drop-down beds, coupled with higher ceilings, why can't we have more versatile floor plans for these shorter "C"s?
A good look of what can be done with a ProMaster/Ducato chassis is what Hymer sells in the UK. They have floor plans with aisle showers, so only the toilet and and a flip-down sink need dedicated space, drop-down beds, floorplans with beds that sleep width-wise and one climbs up on, so bicycles can fit in a storage compartment underneath, and many other things that are nice touches.