I came over to the TT world from the rockcrawling world. I know several guys that have setups like that. I even know one that bought a brand new 30' fifth wheel and without even staying the first night in it, pulled the frame out from under it and built a long enough gooseneck trailer frame for it and his rockcrawler behind it.
We saw this exact same style rig in Cedar Key, Florida in January at a construction site. A flat bed, fifth wheel trailer had an Airstream trailer off it's wheel and springs sitting flat on the deck of the flat bed, fifth wheel and there was plenty of room for construction tools, toys or just a patio above the muck and mire of the ground behind it. Looked like a pretty smart idea to me.
I would say it probably came more from the folks that started with an enclosed cargo trailer and converted the front for sleeping and camping needs. Either way, I love how people come up with cool ways to meet their needs. These days, people dont think or build too much themself.
2006 Ford E350 Van (standard length)
V10, 3.73, 5 Star Tuner, Hellwig Rear Sway Bar, Prodigy BC, Hensley Arrow Hitch