The closes to what you're talking about is likely to be the Volvo 303 with the Autohome "pop top":
http://www.4wheeloffroad.com/featuredvehicles/131_0904_volvo_valpen_tgb_111a_1975/index.html
I started down this path myself, going so far as to purchase an Autohome Airland to graft to the roof of my Astro van before I stumbled on an inexpensive GTRV camper I cannibalized instead.
As others have mentioned, one of the big problems is going to be floor space. You'll probably have to have an access hole (sunroof, etc.) that you can "plug" with a board and mattress so you can sleep over the hole. Check out how the Ursa Minor eCamper handles this problem, it doesn't seem to be a problem there.
As for "negligible benefits", it depends on your criteria. If you use a "Crank Up" RTT like the Autohome Airland, Grand Tour, etc. you could always fit the crank mechanism with a motor (what I had planned), giving you a way to raise the roof and stay out of the weather. The AirTop with the strut-lift *might* also be able to be raised/lowered from inside *if* your access hole was situated in the right spot, etc. This is one of the main reasons I wanted a pop-top - I can pull into a camping spot, slide out of the driver's seat, raise the roof, hit the sack, and even pee in the middle of the night (portapotti) without ever opening the van door.