I don't know if I mentioned this but you could do it with any cab style. For instance, one guy up in Conifer has a 4x2 regular cab dually with a sleeper cab just mounted in the bed. What the previous owner did, the current owner said, (and as I saw) was mount the sleeper, and cut out the entire back of the cab and tie it all in to make it one open space, and like Bill Lins said, this one also looks factory. He has a couch back there that folds into a bed. Pretty nice, but like OTRPU said, it can't be changed back easily, but probably could be changed easier than a frame stretch.
Thats why if I bought a sleeper cab, the only thing I would do is remove the window and put a weather boot between the sleeper and truck cab. That way if I get tired of the sleeper, or need the whole truck bed length, I can take it out. Plus, all I need a sleeper cab for is more storage for short trips. Then I can haul stuff in there, with access to it, plus still haul something in the bed (all 5. 5 feet of it with the cab in it).
Nick