A fifth wheel hitching mechanism is inherently more directionally stable than a conventional "tagalong" or "bumper pull" mechanism. With larger trailers, this becomes a factor, which is why most larger trailers are fifth wheels. But conventional (travel trailer) hitches with built in sway controls and weight distribution can pretty much equal the towing performance that is inherent in a fifth wheel. A travel trailer on a Hensley Arrow hitch is the equal of any towable rig on the road.
As for layout and design, I cannot think of any inherent advantages. There are some travel trailers with high ceilings, 35 foot+ lengths, and all the amenities of a high end fifth wheel. You probably won't see one on a dealer lot cause fifth wheels are more popular in that size/price range, but they are available to order.