Indeed, if I lived in a cold climate, I'd much rather have a vapor permeable but continuously sealed and insulated wall assembly than a vapor barrier.
> So if we wanted to build mold-resistant houses that were designed to idle at 50 or 60 degrees, we certainly could
Totally. Wood framing, plywood sheathing, and drywall's paper backing are prone to mold when exposed to condensation, but those are the most economical materials we have for building. Keeping condensation off those materials at low temps is challenging, and most easily accomplished by heating them along with the space.
OTOH concrete (i.e ICF) is pretty impervious to condensation, although it has other major issues with that make it not ideal for most house walls.
> much of what we do for "climate control" is very ancient technology
Totally++
This is why abandoned houses often don't have much mold to speak of unless you're in a very year-round damp climate.
So if we wanted to build mold-resistant houses that were designed to idle at 50 or 60 degrees, we certainly could.
Most houses should probably have more humidifiers/dehumidifiers than they do; much of what we do for "climate control" is very ancient technology.