Sadly it looks like that idea is not that sustainable. A Passivhaus (well, every current Niedrigenergiehaus, actually) is a very complicated matter and comes with some intrinsic problems:

> Airtight design resulting in draught free construction

That airtight design leads to problems with mold if you have any cold spots. These spots can occur due to construction faults, material faults, or any kind of acquired damage. For instance, you might not even notice that your windows do not shut exactly as they were supposed to after a few years.

In the end, the repair of such a complicated design is again very complicated (especially after a decade or two have passed and technology has again advanced), expensive, and error-prone.

So for me, I'd rather prefer to take an existing, robust and dry building, insulate it somewhat (especially roof and windows) and put in a regenerative heat source (wood, electric) but not to focus too much on the actual energy needed.