Steam/hot hydrogen-lifted airship.
The hot hydrogen cell (a rigid tensegrity structure) would look like this inside the Zeppelin shaped blimp aerobody. The steam has more lift than hot air but less than helium. It insulates the hot hydrogen, which is essentially a vacuum.
edit: thinking about powering it, I lean toward single ducted fans on the tips of the nose and tail that tilt and nod like an helicopter rotor. The varying clearance to the envelope would create thrust vectoring.