I was wondering that too. If I wanted to design a wood-burning apparatus that would be efficient and last 1000 years, I'd use a design that was more like a masonry stove (centrally located on the inside of the house). In any future (I think), a backup source of heat in a cold climate is a necessary redundancy? I would use the most efficient tech now for the burn chamber (rocket?), but also design the burn chamber in such a way to allow for it to be replaced with better tech in the future (perhaps the masonry stove outer structure and thermal bank would support itself - steel exoskeleton? - etc.).